I think there have been many threads about this, but for me:
1. Better notifications, more growl like and not stopping what I am doing and having to respond immediately. Let them go into some kind of queue that I can look at later and clear all of them at once if I so choose.
2.A simple filesystem. I am not asking for access to system folders, in fact, just the opposite. Just a simple shared user directory that shows up as a removable disk when hooked up to a computer. Let all apps access and be able to modify files on that disk and save files to it. This has something to do with my third request...
3. More complete web browsing experience. I am not talking about flash here, I am talking about being able to complete web forms. To be able to use document upload forms (Which would require #2) and more text area fields. The funny part is I cannot submit bug reports or post on Apple's web forums because their text fields do not work in the iPad browser. Plus do some better cache management so I can press the back button and not have to reload the previous page.
4. Better photo handling, I want to be able to organize my newly taken photos on my iPad then import them back into iPhoto/Aperture on my Mac, with those new libraries intact. Right now the iPad is a great viewer but has horrible photo management.
5. iLife for iPad. iMovie is already on the iPhone in a limited form so fix up the interface a little better for iPad and it should be good. Mainly though, I want GarageBand for iPad. There are already multitrack recorders for iPad that work great but they don't have the complete package with sequencing and editing like GarageBand does. Sell it for $10 bucks and intrest in the iPad would increase exponentially in the music community.
Garageband on the mac is known for its simplicity in dealing with a fairly complex subject, that makes it a perfect fit for the iPad. And the iPad would make a great portable recorder for getting a simple idea recorded quickly, then you can easily flesh it out with some software instruments until you can get back to your actual DAW.
So basically, that is what I want from iOS 5.