I believe, and I haven't mentioned this anywhere else yet, not that I can predict these things. BUT... to me it seems painfully obvious.
The last event we had "Back to the Mac" was clearly a play on words. Bringing iOS features back to the Mac. However, I think it was also a pretty big indicator of where iOS is going. Just think about it. Things that were in iOS are now going to the Mac. Meanwhile, it only makes sense to take things from the Mac and move those to iOS... the two will be mostly indistinguishable outside of interface eventually. think about it from a sales perspective. If you can use your iPad, why, you could also use a Mac in the same way. Eventually some sort of save your screen move it to the iPad sort of deal. Or throw your iPad screen on the Mac (think Motorola Atrix but "cloud" based)
So... predictions.
I think it's painfully obvious as well that we'll see a new Notification system being one of the "pillars" that were focused on in iOS 5. It was really one of the last remaining legacy things that really needed a refresh in iOS 4. Needless to say, this is going to be a sight for sore eyes. People will rejoice. It's been a long time coming.
I predict that not a huge amount will change with regard to the iPhone. But this will make a huge impact on the iPad. We will see "Mission Control" from Lion on the iPad.
Just look at the screen shots of it. The icons are huge, great for touching.
It will make the multi-tasking dock a thing of the past. It'll still be there but i suspect it will be there only for the notification system. double tap and you can bring up the "multi-tasking" bar which is now play/pause/skipping for music enabled apps, brightness control and turning certain things on or off (wifi, 3g, etc).
The multi-tasking dock will be moved to Mission Control. With previews of the apps that are running (like the last 4-5) and potentially certain Safari windows so you can jump right to the one you want. Imagine pinching to view individual safari tabs in this view. What I'd really like to see is some sort of card system in this just like you'd see with Palm. But that i suspect won't happen.
Otherwise, maybe a "dashboard" since it is now simple enough to access via Mission Control. There would be your widgets. Maybe those will get the ability to hang out on the main screen, but that seems to Android-like to happen. Dashboard is something they can say "well, we stole it first from Konfabulator, but we made it, not Android."
"Launchpad" is what we think of as the current home screens.
That'll be my prediction anyway.