"If your Design is selected for use by Threadless.com, you acknowledge that you assign to skinnyCorp LLC and its subsidiaries and affiliates (hereinafter collectively "Threadless.com") the entire right, title, and interest in and to the copyright in your Design including the right to sue for past infringement and the right to further sublicense the Design, for its sole and exclusive use on and in connection with the Items. You also acknowledge that you waive all "moral" rights that you may have in and to your Design."
Depends. The music industry as well as the art world are awash in stories about how creators were talked out of their ownership interests. Think the Have A Nice Day smiley or why Beatles songs are owned by Michael Jackson and sold to advertisers.