Prom is a waste of money and is overrated beyond belief. That's really all there is to say
While I somewhat agree with this, I still think it's a good idea to go at least once,
especially if you have a girlfriend.
My school had a junior/senior prom, and I went both years, the first with a girl who I asked out that night at the dance (yes it was romantic, no the relationship didn't last longer than a month) and the second with with my girlfriend of seven months (now a year and seven months). It's as much fun as any other dance (yes if you thought other dances were miserable then this one will not magically be incredible), but it's the added extravagances of prom that make it "special" and a bit more enjoyable. My prom included dinner and a sundae bar, it was located at a country club instead of the school cafeteria, and plus you just feel special in a tux! Also at my prom we had prom king/queen voting right when we entered then we found out who won towards then end of the night. My girlfriend and I won which was pretty special :)
(side note: my girlfriend and I were not considered part of the "popular" crowd consisting of jocks and stuck up pretty girls. At my school, prom was the least influenced by popularity, and I think that was due to our tradition of taking votes at the door with only prom-attendees allowed to vote, instead of the whole school like Homecoming. It could be like this at other schools but maybe it isn't, I don't know)
Anyway my advice to you is have a good time with this girl as well as your other high school friends, dance like a beast, and don't forget to wear protection if you think it will go that far! (but don't expect it to)