To really make the nofollow idea work properly is going to demand that the plugins and tools to work with links inside comments and contributions work on the same level as plugins which right now work with the comments themselves.
In other words, I’m not going to start using nofollow until I can control– easily– which links they are applied to. While I agree with most of what Alex has to say about the naysayers, there is one point with which I firmly disagree. Alex writes, in response to the contention that this attribute will hurt linking between sites:
No, it helps the connections between websites by making them more than simply binary. In the end, people may be more willing to allow outside linking if they know it won’t add to a page’s standing in Google.
The problem is, the reason PageRank works is because those links have a qualitative value. They enrich the entire information ecology, and if a comment contains a good link (or the commenters own link is a good thing), that link deserves to be “recommended” through PageRank. I don’t know about everyone else, but I’ve discovered a multitude of useful information and websites that I now follow through the links in comments and the push that those linked sites received in the Google rankings.
So nofollow is a good idea if selectively applied, and none of the management interfaces work at that level (and, indeed, it seems a lot harder to write something to do so).