I've actually never run into this situation... ever.
I hold all my instructors in such high regard and respect that I just can't see them as anything more than authority figures, or mentors at very least. They could be really hot, and I know a few of them have been, but I just can't get over the fact that they're the teacher and I'm the student long enough to fantasize. -shrugs-
Heck, I'm surprised this has carried over to college. Half my instructors are just graduate-level students who are usually only four or five years older than me at most. Nothing would even really be wrong with us dating if it came down to it, aside from it being against their code... Still, I haven't run into the situation. :x