I like to keep track of the books I've read, but up til now I've just been using flat files stored hither and yon in various dark and unfindable corners of my hard drive. The system on bookhuddle is much, much nicer, themed lists integrated with the tagging system. I'm in the process of building up my lists. Tagging infrastructure makes this really easy, and in going through the process I've already come across (and tagged) several books that seem right up my alley. The ability to subscribe to other people's lists is key. Very cool app.