never. I do occasionaly downvote if someone's being a douche and says something totally uncalled for and horrible, but I've never reported. its not my responsibilty to play dictator and control/ censor what others say or think. the only time I did was some internet marketing dude who spammed every question I clicked on. I don't report actual users though.
on the other hand, I have BEEN reported more than a few times for simple,harmless jokes (ex asking a mormon qa how magnets work etc...) got several answers deleted and wasn't allowed to answers or ask anything for period afterwards...-.- some people just can't take some lighthearted fun, others are just prudes who find everything offensive and feel its their right to get rid of people's opinions just cause they don't agree with em, hence the insane amount of downvotes I've been seeing the last while.
hell, ill probably get a downvote just for this answer too :)
Not too often. I've never reported comments on my answers, or answers on my questions, but if I see someone else getting harassed on here with insults and nonsense, I'd probably report that, if it looks like it's getting bad. I don't think I've done anything about questions though, because usually mods and admin take care of it anyway.
I'm not particularly easily offended. People have the right to express their opinions (however stupid, ignorant, invalid and poorly thought out they may be) and I have the right to ignore them. I'm not really one for censorship, so if I dislike something I usually just ignore it, or comment on it asking for elucidation or something.