There is a CAPTCHA system in the registration portion of the forums, which I'm sure does help with some of the SPAM that the forums could potentially get. Unfortunately, as mentioned above, there are some bots that are sophisticated enough (often using OCR type scripts) capable of getting around many of the CAPTCHA's in use today.
Thankfully the spamming issue is not really the big of an issue on the forums, and often anyone who attempts to SPAM the forums is discovered within an hour. My feelings at this point is to keep the registration process how it is, I really hate (and I'm sure I'm not the only one) sites that have an extremely difficult CAPTCHA that takes me (a human) a few attempts to get around. Personally I rather have an easy to use registration, especially for any new computer users who may be attempting to register.