How often is the subject of comp brought up?

Well, like, pretty often. Unless you are absolutely worthless and you interview horribly they usually will ask you what your preferred salary range is. Or they they will just straight up tell, 'well we pay so and so' or 'we are not paying you shit and you will be our slave.'

Shit man, don't low ball it when you ask for salary. Asking something a little higher than what they pay isn't going to prevent you from getting the job. They'll probably just counter with a lower offer. However low ball yourself, and you may end up biting your tongue. Your call.

What exactly did they ask; how much do you want to be paid? =)

I was unprepared for the question so I left it open by simply saying I was "flexible." I also told my current base when asked. I have gotten to a number of second round interviews before and even then the subject of comp didn't come up. Hence why I was surprised.

Generally you want to do whatever you can to get them to say a number first even if that means avoiding saying what your current comp is. You can't really gain anything by telling them your expected comp or even your current comp.

These questions generally come up after there's been a decision.

As a college student, you don't need to concern yourself with it. The assumption is that unemployment is 14% in the 21-25 year old age group and the standard analyst salary is acceptable for a producer of unknown quality like you.

Illini is right, but at the same time you want to make sure you're not getting screwed. If they throw out a number like $50k at a BB IBD for a front office position, you should know something is up.