On the ones I've seen, he pretty much knows and everybody else is clueless.
Alot of the times, House is clueless. He struggles with the patients' problems then has an epiphany while talking to one of his colleagues who mentions something about his food getting stolen out of his fridge....
...It's a tapeworm! thats why the B-12 isnt getting into her bloodstream!
all in all, it's an entertaining show. Better than watching reality shows. IMO