Unlike the automatic, network-generated last.fm radio, Pandora's music selection is based on manual, human analysis of the composition of each track (see The Music Genome Project). The selections so far have been excellent - it's as simple as putting in the name of a band then listening to the stream of similar music (from a large collection, it seems). Nice interface too. It might be useful to combine the depth of Pandora's musical analysis with AllMusic's mood analysis, for example, as listening to similar music for a long time could do with a bit of variation in the level of 'excitingness'.