Apple has posted iOS 5.1 beta 2 to developers. One new feature is as described as follows:
NEW: Photos taken using iOS 5.1 can be deleted from Photo Stream on your device and will be removed automatically from Photo Stream on your other iOS 5.1 devices. Older photos can be manually deleted from your iOS 5.1 devices.
So images deleted from Photo Stream will be applied across all devices, helping keep your photos in sync.
Check back for updates. iOS 5.1 beta 1 was released back on November 28th.