Personally, I'm okay with it. I agree with Pete Clark that math.SE might not be the optimal source of research topics, and that ideally a student will be guided by the course instructor.
But then again, math.SE may be the best resource available in some cases. I remember being assigned independent topics to present in high school geometry; if only math.SE were around at that time, I may well have gone and learned the basic definitions and a model for projective geometry, which I'm sure my teacher was unaware of.
Although questions of this type lack an objectively correct answer, the math.SE community may be the best source for interesting-yet-accessible topics. Sure, plenty of people will just post their personal favorites, but after a few comments asking about the student's background, I think voting will often push the most helpful suggestions to the top.
So I propose we leave these questions open, as community wiki.