The behaviour I'm seeing is that Shutterfly refuses to print an image, except for as a wallet, unless I'm logged in as admin.
I've put professional photos from my wedding in a G2 installation, and the photographer is cool with people obtaining prints, but wants to protect her digital originals.
For now I'm avoiding a watermark solution, mainly because I don't want to go through hundreds of pictures and manually add a watermark.
Currently it seems that unless people want wallets they'll have to go through an intermediary (me) to get full size prints.