Depends on the concert. Classical music is actually pretty tame and good.
I went to a Tori Amos concert and it was great although I felt veeeery old amidst screaming 12 year olds (her fan base).
The Cure concert was the suxxorz: too loud, too crazy, obnoxious fans...
The Play! concert for Video Game music was great, not too loud, a funny crowd but not obnoxious. Great for laughs though, like the guys dressed as Mario and Luigi. And there actually were people of all ages.
Those were my last 3 concerts. You don't get to go out much after you have kids < rolls eyes >