This thread links to an article you may want to read
http://www.greenguysboard.com/board/...ad.php?t=33048
Might be a good idea to promote the site yourself for a while, fine tune the tour, get retention where you want it.
Another thing to consider is that if you start taking on affiliates too soon, and the tour doesnt convert or the member retention isnt good, the affiliate(s) may leave and never give you a second chance.