I'm 5'2" and agree with pretty much everyone who has said that nothing's worse than the tall people who will push their way in front of you. (This happened to me at Jenny Lewis in March 2006; unfortunately, the sight lines aren't great at Birchmere bandstand.) Admittedly, I like to stand near the front and cannot imagine giving up my spot if I were more vertically blessed. As others have stated, that's the beauty of general admission--if you want that front spot badly enough, you'll wait for hours. If all else fails, there's never any harm in asking the taller person to trade spots; most people are friendly enough.
But oh, I've just decided that the drunk girls who bribe underaged boys with drinks, work their way to the front, and then jump on your foot the entire time are somewhat worse than the tall people who block your view.