By using a custom style that makes nofollow links blink lime, Phil Ringnalda can see how sites are using the attribute:
I'm surprised by how little use of rel="nofollow" I'm seeing (in blinking lime) on non-blog, non-wiki sites. It seemed like such an obvious tool to use, to micro-manage how you transfer PageRank within your site and to other people.
One of these days, I'm going to sue Phil for usurping the color I've chosen for my links and monkeying around with my content to make it more interesting than I intended. Ringnalda v. Cadenhead will become the web dork's Roe v. Wade.