I found out from Linc & Nikki that if you get 100% of the notes correct on a song, you get 5 GOLD STARS!!!! I haven't gotten any of the gold-starred yet, but Travis did a couple last night on medium.
Also, there's an Xbox 360 version coming out with 10 new songs and the ability to download new songs. I don't own an Xbox and I'm not quite certain that I'm willing to pony up $400 for the system, plus the cost of the game and probably new guitars since I'm sure the PS2 guitars won't be compatible with the Xbox. Boo~ !
According to Wikipedia, these are the songs that will be on the new Xbox Guitar Hero: