I meant mainly grad students and the like on their projects, not languages for classes. Languages used for classes are mostly the professor either picking his favorite language for the course (very random) or letting his TAs pick the language (very random if the TAs are not his grad students, mildly correlated with the field if the TAs are his grad students).

Edit: Initially I was talking about undergrad classes, but then realized you might have meant grad classes, so I changed it to say classes in general, which I believe is still true.

Edit 2: I set the delay so I can edit my post a bunch of times after I post it and not provide a moving target.

Edit 3: Clearly you are an exception, but then again you're reading Hacker News.

Edit 4: Where are you going to grad school that doesn't let you pick your own language?