Although Apple is planning to include control over individual photos within Photo Stream in iOS 5.1, jailbreak developer Evan Coleman was able to whip up a useful tweak that keeps iOS screenshots from being added to your iCloud Photo Stream.
Keeps screenshots out of your Photo Stream. This tweak prevents screenshots from being uploaded to your iCloud Photo Stream.
This is personally great for me, as I frequently capture screens from my iPhone for Tips and How-To posts for TiPb but often find my Photo Stream clogged up with a bunch of screenshots I don't need after I'm done. Even though the mod doesn't allow full control over individual photos in Photo Stream, this is a good stopgap until iOS 5.1 is released to the public.
Check it out!
[Free - Cydia Link]
Source: Evan Coleman