Apple has released first beta of iOS 5.1, and in addition a preview of Xcode 4.3 to developers for the iPhone, iPod touch, and iPad. However, the firmware seems not relate to the poor battery performance and Wi-Fi problems.
The build of iOS 5.1 is 9B5117b and the build of Xcode 4.3 is 4D1002. According to the Apple's update notes, the 5.1 SDK to develop code is related to these issues, including iCloud Storage, Movie Player, Music Player, Newsstand, and some Security issues. Yes, don't include the poor battery performance and Wi-Fi problems.
According to iDownloadblog you might not able to downgrade once you’ve upgraded, so jailbreakers beware. And this time Apple skipped iOS 5.0.2 and went straight to 5.1, was thought might be unveiling the iOS 5′s hidden Panorama picture mode or FaceTime over 3G. Just guess, however the jialbreak advice should be considered.
Any way here is the link of the iOS 5.1 ipsw for developers. Read More
via 9to5mac and iDownloadblog