You could enable e-mail validation and add some captchas in the registration to avoid having to moderate all users.

We had daily spam posts on Afterwarp but after installing a plugin to show a random captcha question (e.g. "you have 4 beers, you gave 1 to both of your friends, how many are left?") there was no a single spam post since then! Before that, the other 3 mods and I have been banning at least one spammer/day; I've been prunning about 100 members with failed e-mail activation weekly. :?