I used to go backstage all the time. I was pretty brazen, too. Chatted it up with some cops after a Dave Matthews show while I was on ecstasy. Then wandered backstage and hung out with the band.
I got hammered another time and interviewed bela fleck holding my wallet like a tape recorder.
My taste in music during college notwithstanding, I discovered pretty quickly that if you just walk and don't stop to ask permission, no one stops to try and give it.