Rondavu answered most of my questions, except for the dangerous card question which I read about in Hold'em for Advanced players. Apparently in limit check/calling dangerous boards and dangerous cards is good because if you're beat you're not putting money into the pot and you're inducing a bluff BECAUSE the board is so scary. The guy who misses his straight draw might bluff because he knows you probably don't have the flush draw. Tell me if this kind of reasoning works in NL.

What about when someone reraises you on a draw as a semi-bluff? Say you bet the pot, and now you get raised three times the amount of your raise. Does he have you beat? Is he on a draw?