A source told CVG that the next firmware update is going to contain screen capture. This is yet to be known on how and if uploading them on a server is possible.
A development source has told CVG that PS3 firmware update 2.5 is rumoured to have screen grabbing built in.
This would be a nice feature if it turns out to be true. Capture the greatest gaming moment you have, and share it across your friends on the PSN, or even submit it too a dedicated server, and have people around the globe comment and or rate it. Some games have youtube direct upload support, for example PixelJunk Eden.