You can use the functionality in the mass mailer to do this. Start a new mailing to All Users (you aren't going to actually send it) and then click the "xxx users" link. This should give you a list of all the users' e-mail addresses.
Jason Rhinelander
Gossamer Threads
jason@gossamer-threads.com
Jason Rhinelander
Gossamer Threads
jason@gossamer-threads.com