If you are having issues updating to iOS 5.1, and getting error messages in iTunes about your device not being eligible, there is a quick fix at http://www.iphonejailbreak.me/fix-this-device-isnt-eligible-for-the-requested-build-in-itunes-during-ios-5-0-1-update/ .
I haven’t modified my phone in any way and Apple’s support page is no help (as usual).
