I don't see anyone in my current group-and-a-half cheating. Exploits is a matter of definition – is it an exploit to multiclass bear totem barbarian with circle of the moon druid in order to get the hit point sponge to eat all other hit point sponges? Or are we talking things like 3e's "I jumped so well they made me king" combo (I don't recall the exact combo, but it had to do with a feat that let you substitute another skill roll for Diplomacy because you were so impressive combining with ridiculous jump bonuses for things like high speed and the jump spell)? I've definitely seen the former, but the latter is mostly something we point at and laugh.