I've now had to block six IP's due to comment spamming. Now, when you consider that these spammers are probably using public address spaces provided by AOL, MSN etc... I've probably limited a lot of honest commenters from posting their legitimate opinions and criticisms.
The Psycho Sensei said it best in this lovely post. I couldn't have said it better. I haven't resorted to turning off comments yet, but I'm getting there.