Respectfully, I ask that we not go the CAPTCHA route. It will significantly limiit my involvement. I like posting when I can quickly express my thoughts, but in this day and age of instant gratification on the internet (I refuse to sit through commercials anymore, for example) the extra effort needed to post will make me (and I suspect others) move on.
I've noticed that other forums I've belonged to (music, cartoons, guns, politics, other topics) that have CAPTCHA have fewer members than the ones that don't.
Also, my blog is almost free of comments and I refuse to believe it's solely due to my content. ;)
As for spam, I've noticed one here or there, but I'm not overwhelmed by it (my inbox is different, on the other hand).
Just my input.