Have I gushed about pandora.com here before? In case I haven't: it's a result of the Music Genome Project, in which a large number of attributes were defined and a database of lots of popular songs and their attributes created. pandora.com gives you a Flash-based front end to that database, and once you enter a song or artist you like, it will start playing songs that, based on your input and the database, it thinks you'll like. If it's right, give the song "thumbs up"; if it's wrong, give the song "thumbs down" and it will stop playing the song. In either case, it refines its notion of what you like and hence what it will play for you in the future. (You can thank the RIAA for "thumbs down" only working so many times an hour; they fear that if you can give thumbs down too often, you may be able to cause pandora to play a particular song...and that's a very expensive thing in the RIAA's eyes.)
It displays some discreet advertsing unless you decide to subscribe to the service; I personally have never found the ads bothersome.
So, what's new? pandora.com has decided to start a podcast that goes into some of the theory and how music is put together. The first episode deals with vocal harmony technique, and while it's very much a 30,000 foot overview, it's still fun and educational. Check it out.