It really depends on the theater you go to guys. In my area, Big Newport and Irvine Spectrum are pretty much the only areas you'll find people cheering for trailers and at premieres. Hell, at Big Newport, people bring beach balls and outright party during premieres. Other than that, it just doesn't happen. In Los Angeles, Gruman's and the Arclight (it's not called that anymore) are the two big ones.
So it really just depends on the theater in your area.