See [http://www.google.com/googleblog/2005/01/preventing-comment-spam.html]  
Is nofollow all it's cracked up to be? The general consensus is that it could be helpful, but it's promise is prose to failure in all eventuality. Wether or not it's effectiveness will actually stand the test of time I am unsure. Being on the more conservative side of things, I feel that the attribute is really not that monumental and I don't like it *-* . I, for now will remain a rel="non-follower" of the attribute.