The new feature in this version pertains to Photo Stream and one of the more annoying things with it. Photo Stream is part of iCloud and automatically keeps the last 1000 pictures you took. Unfortunately, there hasn't been any way to delete a single picture from your stream. Instead, you'd have to either kill the stream and start over, or leave the offending picture out for anyone to see. With iOS 5.1 beta 2, Apple has added the ability to delete individual pictures from your Photo Stream and that photo will disappear from all devices.
It's not the biggest change, but it's a good one nonetheless. This version of iOS 5.1 beta is set to expire on January 31, 2012, so there's a good amount of testing time built in before another beta or a full release.
source: The Next Web