just keep 3.2 and then use the PDF patch from cydia!
I'm not sure why you're saying this and why you title it "Important!". I think you're introducing fear, uncertainty, and doubt with that posting.
I'll explain all this SHSH stuff and versions and upgrading and hopefully clear things up.
Apple makes a new version of the iPad operating system available from time to time. In order to update your ipad, Apple does some basic security checks. When you go to update your ipad to a new version, it uses the unique identifier thats hardwired into your iPad as well as the iOS version you're wanting to upgrade to, and generates a "SHSH" key, or unique fingerprint, and saves it on their server. Then it upgrades your iPad to the new version. The reason it generates this SHSH file is so that it records the fact that your machine was updated to that version and therefore is authorised to restore to that version in the future. Of course, if Apples doesn't want you to be able to restore to that version in the future, they are in control and simply won't allow it.
Assuming that they are ok with restoring that version, if you want to restore your iPad in the near future, it looks at your unique identifier and checks it's servers to verify that you have previously installed that version. It then restores your ipad to that version.
So just to be clear: When you update your iOS, Apple generates a SHSH file and saves it on their servers. It's their way of recording that you updated. Then in the future if you want to restore, it uses your machine's unique ID to find the SHSH file on their server. If it isn't there, then you must never have installed that version and therefore you're not allowed to restore it. If it's there, you must have installed it previously, and therefore you can restore it (if they want to allow you to).
Ok, all good.
At some future point, Apple comes out with a new update. At the same time, they stop making the older version available. From that point on, when you do your update, it will go through the same steps as before and will generate a new SHSH file based on your unique identifier and the (new) iOS version. Note that this new SHSH file is based on the NEW version of iOS. They won't generate an SHSH file for your current/old/previous version. If you didn't update to that previous version before, then there won't be an SHSH file for it and never will be. So, for example, when I bought my iPad it was on version 3.2.1. I can't use iTunes to recover back to 3.2, because I never updated to it in the first place and there's no SHSH file on record on the Apple server. So I can never "restore" back to 3.2.
So if you want to restore your iPad to any previous version, you must have previously updated to that version via iTunes so that Apple generated an SHSH for your iPad+that version of the iOS.
Now quite often, even though you might have previously updated to several versions (like 3.1.2, 3.2, and 3.2.1), Apple will usually only let you restore back to the newest version even though they've got SHSH keys for all 3 on their servers. They may do this because they don't want you to be able to go back to the older version (because it's hackable or has some major bugs etc.). Apple's in contol of what versions you can restore back to.
Ok, fair enough. So that's a generalised overview of what happens when you do normal updates of iOS for your iPad.
Now here's how the jailbreaking recovery stuff works:
Let's say you were originally on version 3.2 of iOS for your iPad and Apple comes out with 3.2.1. You upgrade via iTunes and you're now on 3.2.1. ok, Apple generates an SHSH file for 3.2.1 and saves it on >their< server. Then, some months later, Apples makes 3.2.2 available and you upgrade to that. They also make 3.2.1 unavailable from that point on. So on the Apple server, they have an SHSH keyfile for your machine for 3.2, 3.2.1, and 3.2.2. However they decide to not make 3.2 or 3.2.1 available to you, so the only option you have when you want to restore/recover is to go to 3.2.2. Which means you're not happy.
BUT: What Cydia does is pretty clever. When Apple makes 3.2.1 available, you can use Cydia's "Make my life easier" button (or whatever it's called), and it will then use your machine's unique identifier and go to the Apple website and pretend to be your machine and ask for an update. Apple generates the 3.2.1 SHSH file, and Cydia grabs it and saves it on it's own server. It does this because it knows that one day, Apple will make a new version of iOS available (like 3.2.2) and once they do that they will stop generating SHSH files for 3.2.1 and not make it available. Only Apple can generate the SHSH files, and these files are needed to do any restore.
So now Cydia has a copy of the 3.2.1 SHSH file and they nicely keep it there in case you might want to use it.
So then you decide to update to 3.2.2 via iTunes, and discover that you won't like it or want it. ITunes won't let you roll back to 3.2.1 because they've decided not to let anyone do that. And you can't restore back to 3.2.1 without a 3.2.1 SHSH file. And you can't generate a 3.2.1 SHSH file any more via iTunes because 3.2.2 is now out and Apple will only generate a 3.2.2 SHSH file.
But that's where Cydia comes in. Because you used the "Make my life easier" button back when 3.2.1 was still around, Cydia was able to make/take a 3.2.1 SHSH file from Apple and save it on their server. So even though Apple won't make theirs available, you've got Cydia's copy.
Now it gets a bit tricky. In order to do a restore/recovery of your iPad, iTunes needs a copy of iOS 3.2.1 AND it needs to check it's server to see if there's a valid 3.2.1 SHSH file for your iPad. And of course, it checks to see if it even wants to allow you to go back to 3.2.1. And we know in real life, now that 3.2.2 is out, Apple will NOT allow you to roll back to 3.2.1 and tells iTunes this, and ITunes politely tells you that you can only recover to 3.2.2.
And you don't want to do this, because 3.2.2 wasn't jailbreakable or had some feature you don't want. (As of mid-September, it's apparently now jailbreakable but possibly still a bit hit-and-miss).
So in order to restore back to 3.2.1, ITunes has to be fooled into thinking it's ok. ITunes goes off to it's server to see if you're allowed, and it then needs a valid SHSH file. And of course, if it gets past those 2 checks, it then needs a copy of 3.2.1 iOS to use for recovery.
Well, we know that Cydia's got a copy of your 3.2.1 SHSH file, but we still need to fool iTunes into thinking that it's ok to do all this. ITunes checks a server called 'gs.apple.com', so what we need to do is redirect ITunes to another machine that pretends to be gs.apple.com. This pretend machine then says "Yeah, 3.2.1 is ok, go ahead, and here's the 3.2.1 SHSH file to prove that his iPad is ok."
For this to work, the fake gs.apple.com server needs a copy of your previously generated 3.2.1 SHSH file. And we know that Cydia kept a copy of that.
This is where problems come in for the poor souls that didn't get Cydia to save a copy of the 3.2.1 SHSH file at the time it was able to. Unless you used that "Make my life easier" button back when 3.2.1 was available via ITunes, then Cydia won't have a copy of it and thus there's no way to proceed with the restore. Even though we've redirected ITunes to a fake gs.apple.com machine, it still needs a valid 3.2.1 SHSH file to be able to continue with the restore. So unless you got Cydia to save it back then, you can't proceed with the restore.
So that's why a lot of people that buy a new iPad run into problems. The new iPads are running 3.2.2 or even newer. So there's no way to now generate a 3.2.1 SHSH file since Apple won't do this and nobody else can. So a 3.2.2 user can't go back to 3.2.1 because there's no 3.2.1 SHSH file.
(Note: There are a few threads talking about how to go back from 3.2.2 to 3.2.1which I haven't yet read, so it's possible that there might be some new way I'm not familiar with. But at this point, unless they've found a new way, it's not possible).
Ok, so assuming you got Cydia to generate a 3.2.1 SHSH file back when it still could, then a restore/recovery back to 3.2.1 is going to be possible. Itunes will talk to gs.apple.com, get fooled into talking to a fake one that says "yes, it's ok to restore to 3.2.1", and the fake gs.apple.com machine will provide the previously-generated 3.2.1 SHSH file, and then Itunes only needs a 3.2.1 iOS image to start the recovery.
There are a few different ways to go about doing the recovery which I won't go into here. One way is to install TinyUmbrella, which will grab the SHSH file from Cydia and set itself up to act as a fake gs.apple.com server. You then just have to find a copy of 3.2.1 iOS image on the web and run ITunes 'Restore" via the shift-click method (if you hold down Shift while clicking Restore, it will prompt for the location of a valid iOS image file on your local hard drive). Recovery proceeds from there.
If you've read this far, it's only because you haven't understood how the whole SHSH and recovery process works in the past and were looking for a clear explanation. Hopefully I've provided just that. I'll keep an eye out for any corrections or comments from people if I got any of the above wrong. I think conceptually it's pretty accurate. I haven't bothered getting too technical as it's not necessary to understand to that level just to get things working.
Bottom line; Use Cydia's "Make my life easier" button at least once so that it stores your iPad's unique identifier on it's servers and so it can then go to Apple's servers from time to time to generate new SHSH keys. You can tell what keys Cydia has got available by simply starting up Cydia on your iPad. It shows as small reverse-coloured text above the "Welcome to Cydia" banner and below the top bar. If there's nothing there, you haven't used the "Make my life easier" button, or Cydia hasn't yet gone to the Apple site to generate the SHSH files. You will also notice from time to time that it's generated new keys or is in the process of doing so.