Hi, I'm using confirm-user-registration plugin to force manual confirmation of users. Our last forum (using Joomla) had a serious spam problem despite a Catchpa.
It's working great but one user suggested that I auto-confirm users whose e-mail addressi are from a certain domain (iastate.edu in our case). I would still have to do a little spam filtering for 'bots that get wise to this but it would be nicer to new users.