I like iOS 5 -- a lot. It has several strong improvements over the already-good iOS 4, such as notifications, improved AJAX support in the Safari mobile browser, and wireless syncing (both via Wi-Fi and through iCloud, which I believe will quickly make anywhere, anytime access an assumption iOS users impose on everything); thus, iOS extends its lead over Google's Android and other mobile OSes. But it's by no means perfect.
Given that Apple keeps iOS updated regularly, here are what it should be working on for one of the next versions. Some of these are old requests -- odd omissions that seem less and less supportable, considering the other capabilities in iOS 5 and in the new iCloud service.
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1. A "return to app" gesture. iOS 5 brings Mac OS X Lion-like multitasking gestures for navigating among apps without needing to use the Home button. For example, a four-finger sideways swipe moves you to the next or previous app that's running (depending on the swipe direction), and a four-finger swipe up exposes the multitasking dock that shows apps in operation and has controls over iTunes, AirPlay, and rotation lock or mute (whichever one is not set for control by the side switch). Then there's the four-finger pinch gesture to open the home screen. But there's no easy way to return to the app you were running before you opened the home screen. When the home screen is visible, the four-finger swipes simply scroll the home screens. How about designating the four-finger expand move as the "return to app" gesture?
2. Support for group creation and editing in contacts. One of the main uses of a mobile device in the field is communicating, which includes managing the information on the people at the other end of the line. It's very odd that iOS 5 still doesn't let you create and edit groups in the Contacts app, and it still won't let you send an email to everyone in a group by entering that group name in the To field; instead, you have to select each person in the group separately. iOS 5 imports groups from Exchange, Outlook, and Mac OS X's Address Book. You can edit every other attribute of your contacts and even link cards (such as for spouses who have different last names) -- so why not groups? iOS 5 finally introduced album creation to the Photos app, so I don't see why it won't do essentially the same thing for contacts.
3. Customized email signatures per account. As smartphones and tablets are increasingly used for both work and personal purposes, having a single email signature for all accounts handled in iOS's Mail app makes no sense. You should be able to set a separate signature per account, just as you can in Apple's Mail client in Mac OS X -- or in Outlook in Windows and Mac OS X.