At Stampeaz, we promise never to trade, rent or sell your information to any third party, online or offline. Period.
Full disclosure: Stampeaz has been known to help relay special gifts from known users (for Secret Santa exchanges, etc.), without revealing any personal information or where they were being sent, though. :) If you don't want this to happen (what? you don't want surprise treats in the mail?), just say so. :)