There's been much discussion about this in the last few days. Bernhard Seefeld (the man behind the great map.search.ch) has a good point in saying that some community request for comments could have made this much better.

Why not take the opportunity to give more semantic meaning to weblog comments for example, instead of blindly nofollowing everything?

Bernhard links to Ben Hammersley who thinks this might actually increase the comment spam activity, as lowering the efficiency of a free thing should increase the use of said thing. Makes sense to me.

Let's hope our not-evil giant thinks a second time about this.