I haven't played Guitar Hero yet (I am later tonight), but from what I've heard, it gets really hard. Some people put a lot of time and effort into playing the top level songs on the hardest settings. Is it a comparable amount of time and effort to that of learning to play a real guitar? If it is, the difference is what the results are. The former, you can show off to your friends that you can play a tricky game. The latter, you can play music, maybe even compose your own music and create something you can present to the world and possibly gain a profit form. But, the majority of people who play Guitar Hero don't play it this vigorously, and playing a guitar-themed video game does not mean you have an interest in actual guitars. So, in the end, comparing the two is stupid, even though it'd be cool if more people knew how to play the guitar.