Apparently, it's a good idea to "collect a contributor license agreement 
(CLA) from each person who works on the project, explicitly granting the 
project the right to use that person's contributions."

http://producingoss.com/en/copyright-assignment.html

Not the same as a transfer of copyright,  mind you.

See also issue331 and issue176.  It may be good to kill several birds 
with the same stone here, sending out requests for CLA, and also giving 
users the option to do copyright transfer, making it clear that we do 
not require the latter.

I'm not a fan of this kind of thing either, but it seems better to 
attend to this kind of stuff sooner rather than later.