Apple has released iOS 5.1 beta to its registered developers which is compatible with iPhone 4S, iPhone 4, iPhone 3GS, iPod touch 4G, iPod touch 3G, iPad 2, and iPad.
At the moment no details are provided through release notes that what changes iOS 5.1 beta includes. So download and test it and provide your feedback about it through comments.
Alongside, iOS 5.1 beta update XCode 4.3 (build 4D1002) is also available to developers for download.
Download iOS 5.1 Beta