Most people that register on Dolphin sites are hit and run, actual persons and not spam bots. Captcha and anti-spam questions won't stop them.

Email confirmation during registration might help reduce spam, but email confirmation can also drive you nuts. Believe me, people can be pretty stupid and many times can't figure out how to get through the registration process if you require email confirmation. I have a vBulletin site where I state in gigantic bold yellow letters that you must visit see more a link that was sent to the email address you registered in order to activate your account. The idiots will still try to register with bogus email addresses and then complain that your site doesn't work. I don't know how some of these people find their way home. Another huge problem with confirmation emails is that services like aol and yahoo will block the incoming email as spam and the user will never receive the email they are supposed to reply to, and the account never gets activated.

Blocking IP addresses must be done with caution, since many users will be accessing your site through proxy servers.... aol, etc.

The vast majority of spam originates from .cn, .tw, .ru, and a handful of other top level domains. I plan on eventually using GeoIP to block entire countries from accessing my domain.... if english isn't their primary language, they don't need to be on my site.