Since what happens in Vegas stays in Vegas I'd imagine just about anything and even more than that goes.
Seriously, in my opinion people make way too big a deal about this. Just don't be a friggin' idiot and you'll be fine. I've done everything from emailing in advance to just showing up for class (probably what I do most often). I've yet to meet a teacher which wasn't cool with it although some of the students can get fussy and self-important about the whole thing. Of course I'm in the Bay Area so your mileage may vary.
The advantage of emailing or making contact is that you won't show up on a night when they don't even though the web site said they would show up. Or, you won't turn right, drive around in circles through a very bad part of town because Map Quest is fallible after all. Been there and done that!