tags at ORblogs
You've probably seen tags in action at del.icio.us, Flickr, Technorati, and Metafilter. (The kids are calling them folksonomies.) I set up a similar tag folksgeist page at ORblogs called ORblogs tags. The difference between del.icio.us et al, and ORblogs is that the Oregon Weblogs tag page is using categories that were found in RSS feeds. So while not technically tags, the effect is similar. And I think if people started aiming their weblog post categories toward a group goal, interesting things would happen.