No, I have a real strong feeling that Snape's offing of Dumbledore was not as it seemed.
Snape may turn out to have been a good guy all along.
I kept thinking that at the end of the sixth book. Dumbledore could search for the remaining horcruxes more easily if everyone thought he was dead.
I'm afraid Snape IS a good guy.
It seems pretty obvious that Snape killed Dumbledore because Dumbledore wanted to be killed (apparently he'd been horribly maimed and cursed in the search for Voldemort's whatchamacallits...) AND it would get Snape into Moldywarts inner circle. Snape also refused to kill, maim or carry off Harry Potter when he had a chance.
He's a good guy.
Snape may turn out to have been a good guy all along.
I had the same conclusion after reading the last book. Several other Potterheads have said taht, too.
It's going to be interesting.