I expect 4.3 available to everyone tomorrow, iOS5 Preview (Beta 1?) available tomorrow to developers, released this summer alongside Mac OS 10.7.
I think the event will be like this:
1. Sales updates - Verizon iPhone, iPhone in general, iPad sales, iOS sales in general.
2. iOS 4.3 info
3. iOS 5 info
4. iPad 2 as "One More Thing.."
Just my guess.
I am of the view that unlike many other Apple timetables which are tried and true (e.g. Timing of the new iPod touch each fall), ios previews and updates are a sufficiently new phenomenon, and are impacted by an increasing number of recent new and different wrinkles (first the iPad, then the Verizon iPhone) that we shouldn't just look to the past to draw overly firm conclusions.
Is it likely that iOS 5 gets previewed this spring some time? Yes it is. But many things, including those mentioned above, could serve to continue the trend to push it later into the spring each year.
To sum up, my guess (and it is a guess therefore 99.9% certain this will be wrong) is we'll see four things tomorrow:
1) iPad 2 with a VERY short lead time before launch.
2) A preview of some iOS 5 features in the same way they previewed Lion but NOT a full-on walkthrough. That can wait for a developer event where they can have more time and, if they really are going to launch iPad 2 almost immediately, start building hype up after the initial sales rush has died down.
3) Some info on iTunes going to the cloud in some form or another.
4) A MobileMe announcement.
All four of those would link in together to form a very nice message about the future of iOS AND OS X and play very nicely off the tag line of "come see what 2011 will be the year of".
why would the ipad 2 be the one more thing. if anything i can see ios 5 being the one more thing.
this is the biggest problem ios faces. one device comes out at the begging of the year and has to wait till june or fall to utilize the update. there needs to be some ipad ios only items that make the 4.1-4.9 releases compelling.
If the even tis focused on iOS 5 then I think it will be the "One more thing" like the redesigned Macbook Air was when they were talking about Lion last year.