lol me and the wifey do spin class every week. good cardio, i burn about 800 calories in that hour.
we dont do anything like that tho haha...

basically the bikes have a little screen and a lever that controls the gear. instructor will call out a gear and a RPM, whether to sit or stand upright or down low, usually to the tempo of the music.
i actually think spin class is great exercise...roughly the same as doing a very brisk 20 mile ride. but it all depends on how cheesy/corny the instructor/music is though, ive been to some and i just couldn't handle the instructor and their bad music.