What sort of OS update do you want?
Honestly, I don't know. Everytime I sit down and think 'How could I redesign the iOS UI?' I can't come up with any better solutions.
I don't think throwing all of your apps in a menu or a folder or off to the side is a great solution. They're all still there. I know a lot of people want widgets or something and I can see the appeal but I'd never use it.
But I am tired of looking at rows of icons after 4 years. I'm also tired of having to worry about holding off doing upgrades until I can jailbreak just so I can install BiteSMS. It's way too much work. If iOS 6 looks exactly like iOS 5 but they include some kind of better systems for text messaging (quick reply, PLEASE), I'll jump all over it.
I was also not a fan of MobileNotifier and, thus, am not a huge fan of iOS 5's notification system. I think the Notification Center is a bit of a kludge and ot even really necessary. I do like that Apple has widgets (stocks and weather) and I think that it was more of a test and that we'll see them open the Notification Center to 3rd parties in iOS 6. But I changed my text messages back to the alert style because I just liked it better.
I'd LIKE quick setting toggles for like WiFi/Bluetooth, etc but don't think they're really necessary. iOS does a fantastic job of managing these on its own, I think and the only times I need to toggle them on/off is if I'm having some kind of other connectivity problem. But I just throw it in Airplane mode and then out and it resets everything and that doesn't take but a couple of seconds so it's not a big deal.
I'd like to be able to exclude accounts from the unified inbox, but that's more of a mail.app issue than a iOS issue.
I'd like for the App Store to not throw me out whenever I buy an app. Yes, I know I bought an app, you don't have to show me where it's at. (I think this is aimed at more novice users though so I kind of see the point).
I wish I could remove crap I don't use from the home screens. Like Poof! I could get rid of half of the default icons and I am still able to use them if I search for them.
Speaking of search, I'd like to have search add-ins so that I could like search for something and then be able to select like 'IMDb' and have it open the IMDb app.
One request I did give to Apple through the feedback form was to show a countdown timer on the lock screen. For instance, if I cook steaks, I know exactly how long each person likes theird cooked. So when I go to check where I'm at, I have to turn the phone on, slide to unlock it and can then see the time remaining. I think if you have an active countdown timer you should be able to see it just by waking the device up.
I'm sure there's a bunch of other little things and, as I said, I don't think i really KNOW what I want. I just know I want something a little different.