The Geeky Guts of It All
For the really geeky, the new plugin changes the behavior of links in the tags <MTPings>, , and and, far cooler, also lets you enable the automatic tagging of "nofollow" to any URLs encountered in any other MT tag by adding the attribute nofollowfy="1". Are you tired of the links in your articles themselves giving other sites PageRank? Then you could use and it'll never happen again. (Though I don't know why you'd do this, honestly!)
I've installed the plug-in on my weblogs; if you're so inclined, pop over to my AskDaveTaylor.com site, find one of my articles with comments, and use View Source in your browser to confirm that I do indeed have the snazzy new rel="nofollow" attribute in comment links off my site.