that facebook login on external sites is starting to look like a brilliant move. one of the greatest obstacles to signing up new users for a site is initial authentication (i.e. create a user name, password). with facebook as the turnkey to all these new sites, users feel reasonably safe when backed up by the their fb user name and password. for instance, i was checking out this site, and then realized just to check it out, i wouldn't have to do any signup. that definitely makes a difference. same thing for yahoo, and other similar sites.