The new version of movabletype (2.66) includes a feature to prevent someone from flooding you with comment spam. A change I think is more important, however, is this one:
Also in 2.66, we’ve changed the behavior of <$MTCommentAuthorLink$> to use redirects when linking to URLs given in comments. The goal of this is to defeat the PageRank boost given to spammers by posting in the comments on a weblog.
Once 2.66 and higher are out there, the value of comment spam drops considerably. I don’t think the people posting comment spam are expecting lots of hits from those comments. They’re doing it for the PageRank, and this change nullifies that.