Yes, of those who are inclined to go out/party, they do so quite a bit at my school. I don't think it's much different than if you were working a normal 9-5 job, 5 days/week, i.e., Sunday-Thursday night are pretty low key, with maybe one or two nights taking a couple hours to go to a friend's place for dinner, go out to eat and a few drinks nearby with some friends, or maybe going to a nearby bar on Thursdays (the remainder of the nights are spent in, doing whatever). Friday and Saturday, I usually go out both nights to clubs, parties, bar hopping, etc.
Biggest difference from normal people out in the work force just comes during the week/weekend before exams, when people are pretty buckled down and forced to study.
For the record, though, my school is P/F, no internal ranking, and exams are usually on a block schedule (i.e., we'll have exams for whatever classes we're taking clustered together, then will have 3 or more weeks with no tests to study for), so there's likely less pressure than at schools where you're graded or have an exam every other week. I'm an MS2, and I have no doubt that the "partying" will be pretty dead next year 🙁.
Also, to comment on the above post where someone said not to expect a 180 from undergrad, I strongly disagree. It's more about what you like to do. In undergrad, I became unfortunately obsessed with studying and had next to no social life. It wasn't because I didn't like to go out, but because pre-med neuroses took a pretty strong hold of me. I wasn't particularly happy and, by the time I got to med school, I promised myself I wouldn't do that again and that I'd enjoy myself--P/F and a new perspective really helped this.