When I read the book my first impression was that Snape was evil, then after reading the fight scene I was thinking maybe he's not, then I read JK's interview on Mugglenet and I am more certain that Snape is evil! She says some stuff like Dumbledor is human and humans trust when they shouldn't and stuff like that.

So in the end I think that Snape is on the dark side and Dumbledor is dead for good (although I am Greatly saddened). JK has also said that you can't come back from the dead. I say this assuming that Dumbledor really did die when Snape cursed him. If he didn't die why would his portrait appear in his office? Why would his spell freezing Harry end at that moment, Why would Fawkes sing?

There's another question to. If as Harry said in the book, the spell ended because the caster had died then wouldn't his spell of protection at the Dursley's end to?