Scott Andrew's doing an interesting thing with the open source version of KnowNow's auto-updates-to-the-browser event router thingy (Scott has a good overview of how it works).
I built something using KnowNow's stuff a couple years ago. It was long before it was open source (and probably less mature). It was a project to demo their technology that worked with Blogger and blog updates. I didn't finish it, because the project got canned, unfortunately. But what was there was pretty neat—and crack-like addictive. I've been wanting to dig into it again since they open sourced. So much fun stuff to build, so little time.