Rel Equals Nofollow.
It’s about time. Several major search engines are adding link no-follow support to combat comment spam. For years we’ve been able to tell search spiders to ignore an entire page, but there’s been no way to tell them to ignore just one (or several) individual links on a page. Now we can, by tagging each untrusted link with rel="nofollow".
Now you can write a news article or weblog entry containing links you care to promote (by allowing Google/Yahoo to increase their page ranking) while forcing any content supplied by readers (i.e. comments) to be ignored by the search engines. No reader-supplied page-rank-boosting links → no more comment spam. Done and done.
More coverage: ArsTechnica, Dave Winer, eWeek article, MSN, Google (entry removed for some reason).
Update 1/20: Of course, removing the incentive to do something doesn’t cause it to disappear immediately. I’m tracking the opposition to nofollow on a more recent weblog entry.