Perhaps, I must admit that scene did make me a little sceptical, but perhaps there was another reason for it. Harry was about to run off to the staff room and thus, waste even more time in his search for Dumbledore, when Snape appeared. His hatred undoubtly clouding his judgment at the time, however, he did get Dumbledore's attention through the screaming match and saved Harry alot of time without appearing that he had helped the boy. Or maybe I just like making up piss poor excuses for Snape too much
He treads a very fine line though, reguardless of which side he is on. And because he his undeniably intelligent and very good at hiding anything he does not wish the world to see, I don't think we'll find out who's side he is on until the very end. Either way, he'll still be my favorite character
Mind you, you could be just being a true Slytherin and doing whatever it takes to survive the war. Thats the thing with Slytherin though, he could be on either side, or playing both sides, and still be true to what JKR described Slytherins as being - cunning, ambitious, means justify the ends sort of people.
I still reckon he's got some psychological problems - namley his hatred of himself - and of course, his paranoia. All in all, he's an interesting bloke though.