My brother, who (like me) uses Blosxom for his website, has reminded me why I gave up on comments on this website. Michael writes:
664 real comments on this site, 18361 I manually said no to, 32111 were blocked based on originating IP, and 5007 contained a bad word. Andrew currently donates 506 mb of disk to hosting just comments.
My experience with comment spam was similar -- and it took more time than it was worth to try to block the spammers. Even now, when I look at my website log, there's a huge amount of traffic from spammers trying to use long-disabled comment links.