High Schools around here use songs as themes. My son didn't go this year, but he did say last year the theme was fun! song "We are Young". (he didn't go either, but remembers the voting)
My theme (from the dark ages) was a Phil Collins song- We said Hello Goodbye. My sisters prom theme was Bon Jovi's Never Say Goodbye.
A former colleague told me her childs theme was in 2007 so it was a James Bond theme.
I think around here there are so many themed functions (bar/bat mitzvahs, sweet 16s) they just use popular songs instead of props and decorations.
I think the committee picks around 6-8 songs, the class votes, votes again if necessary and there you have your theme.