As you can see, there are 591 songs available for Harmonix's Rock Band "platform". But did you ever wonder how many are hard and how many easy? Or which genre is most represented?
Pwn or Die did, so they sat down and started taking notes. At the end of it, we have not only statistics on the game's song library, but statistics represented as graphs. And everybody loves graphs. Especially rock n' roll graphs.
The one above, showing the musical genres represented in the game, is probably the most interesting, even if it is also the most contentious (as genre classifications generally are). There's a few more - including breakdowns of songs by decade and songs by difficulty - at the link below.