So, how much is a normal rent increase per year? I'm looking at an apartment that a friend of mine currently has--but the rent is going up $100 in the year for when I'd take it over. This seems kind of extreme to me, but I've never lived in an apartment before...Any words of wisdom?

It is much easier to raise the rent on a new tenant, versus a person who lives there year to year. It is a pretty typical move, just ordinarily you'd have no idea you were paying $100 more than the last guy. Tell the landlord you know what your buddy paid, and see if that makes a difference.