Do NOT buy one before the update.
I just got one a few days ago (borrowing from a friend) and i'll explain why you should wait.
1) It is quite slow and stuttery. Viewing PDF files with iBooks, goodreader, or papers, when switching pages and zooming in/out, you get a lot of lag, stuttering, and checkering of the screen. In a lot of games when starting them up and using the menus, there is little bits of lag and stuttering. Even when using the main menu's/settings, there is stuttering/lag. It feels slower than my android phone.
The games in general run really well, no complaint there, but it feels like they are really pushing the hardware to the max. Infinity blade looks amazing on the iPad, but it won't get any better than that, and even then it stutters sometimes.
Having the PDF files load and transition smoothly with no lag, stutters, and checkering would make the experience much more fluid and seamless, and simulate better the feeling of reading actual paper and not a screen. As it is now it's not that great. I think the second generation with faster hardware and more ram is REALLY going to make a difference in the user experience over the iPad 1, even for the stuff that is already out. After using the iPad for a week (and not just in stores) it's very obvious that this was an experiment by apple, and now that it has been massively successful you can bet the iPad 2 will really take the experience to where it should be.
The iPad 1 is already lacking in ram/speed to just do simple mundane things in a smooth and seamless manner, and so imagine in 6-12 months how you'll feel when all of the new apps run poorly (the current ones generally run very well, but as I said they are a bit laggy sometimes).
I had this huge feeling of gadget lust because the iPad is to 'cool', but trust me as soon as you get it that feeling wears off and you're left with the reality of your purchase. You are left with the fact that you need to use it for the limited functions it can perform, and that is it. It is only an app launching platform, and is only as good as the apps, and for the iPad 1 it is lacking in ram and speed to be able to give you an optimal experience for this. Also as people have mentioned, the iPad is a tad on the heavy and big side. Even a little bit lighter and smaller I think would make a big difference in the long term, and make it more comfortable to use.
Many people may disagree, but they are wrong and deluding themselves. It's easy for me to be honest because I didn't sink any money into this device and I don't need to justify my purchase to help me sleep at night. It's an AWESOME device, with some really great fun apps, but it is lacking in what it should be. The iPad 2 will really be great, because even the same stuff the iPad 1 can do is pretty great, it just needs to be faster, smoother, and have more ram for caching things and not checkering the screen.