I guess I should mention that I do consider myself an actual musician... I'm a bass player (upright for school, electric for personal use). I also own an acoustic and an electric guitar.
Whether or not this has anything to do with Guitar Hero, I'm not certain. It certainly doesn't hurt.
Most people say there's very little connection between playing an actual instrument, and the fake guitars in games. Though it does help you get a sense of rhythm.
Rock Band however, there's a pretty good connection between the drums and real life. If you can play drums in real life, you can do RB pretty well, and if you do good (as in, you can 5 star everything) on expert drums in RB, you have the potential to play real drums to an extent.
Oh, in my opinion, GH > RB. RB is fun and all, but it's got so many flaws... the only saving grace is that it's fun to play with a group of people, and that the drums are fun. However, the instruments they supply are incredibly shoddy (I broke my drum peddle within a week) and feel weak. Plus, the guitar and bass lines are insanely easy to do, with the exception of certain solos, which become impossible due to how tight they've made the system of Hammer ons and Pull offs. Which kind of is fixed if you use the solo buttons on the RB guitar... but since that guitar is near unplayable anyway, it means those sections are death. Plus, the graphics are pretty ugly... the charts look horrific, and seeing HoPos is incredibly difficult. The people move very fluid like though.
