When Apple launched iCloud and its Photo Stream service, there was a glaring omission: Apple didn't include the ability to delete photos that had been uploaded to Photo Stream. This was a problem that could potentially lead to some embarrassing situations.
There was actually a roundabout way of deleting photos from Photo Stream, but it required you to delete your entire Photo Stream, which wasn't very convenient. When the iOS 5.1 developer preview was released, the ability to delete individual photos had been added. There was hope!