The best I see is this checklist:
http://developer.apple.com/devcenter/ios/checklist/
Excerpt: βExisting applications in the App Store and those created using the iOS 4 SDK must be run on iOS 5 without changes. However, you must test your existing applications running iOS 5 to be sure that there are no problems compatible. 5 works with iPad 2, iPad, iPhone 4, iPhone 3GS, and iPod touch 3rd and 4th generation. "
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