The big three, Google, Yahoo!, and MSN (I bet you thought I was talking about cars) have implemented rules for NOFOLLOW. A good explanation can be found in this article from ResearchBuzz!. The article gives a pretty nice explanation of how comment spam works, as well as this current method to address the problem. Links to plugins for some common blogging programs are also included, as well as links to NOFOLLOW announcements from the big three.
Unfortunately, the article does not paint a pretty picture for the future. This method of controlling comment spam may work for now, but we may be beginning an “arms race” against those spammers. The blogging community may implement a new measure, and then the spammers may strike back. I imagine this will be a never-ending battle as two opposing forces square off. One positive may come from this battle, though. At least the programmers (on both sides of the war) will have job security.