The original concept of using rel=”nofollow” to combat blogspam or splogs was a good idea when originally proposed by Google.
This was to identify links that should not be counted as a vote or endorsement by the linking page. It’s interesting to note that it was originally designed to be utilized on pages where users or visitors could add links by themselves such as blog comments, guestbooks, visitors stats or referrer logs.
I’m seeing more and more comments on the expanding use of this attribute by some search engines, especially in relation to paid links or text ads placed on a site.