I'm often of the paranoid/pessimistic mindset that, at some point in history, every possible appealing combination of notes was exhausted, and now we're all just running on subtle variations of the same catchy themes (but hey, given the way the rap/radio/recording industry works, can you really blame me?). I mean, if it hasn't happened yet, though, it has to happen eventually. Heck, I've tried writing a few songs myself--the lyrics are certainly unique, but too often a tune I think I've come up with is really just based on some riff or chorus from a ditty in the recesses of my memory.