The second beta for the upcoming iOS 5.1 update has been seeded to developers. The big change in this update is the ability to delete individual images from Photo Stream. Currently, when you take a picture on an iOS device, Photo Stream (a feature in iCloud) automatically syncs it with all of your Apple devices. With iOS 5.1 beta 2 onwards, you can manually delete an image on a device running this update and it will automatically get deleted from other iOS devices running this update.
GSM Arena, Apple releases iOS 5.1 beta 2 to developers