It's been pretty smooth since setting up reCaptcha. As much as people criticize it, reCaptcha is basically the savior of server admins. None of the other options I tried had any effect. Blocking bad IP ranges, honey pots, skill-testing questions. Bots found ways around all of it.
reCaptcha was so effective that for a while I was worried that registrations were simply broken. Had to create a test account just to make sure it still worked.