The evidence of Dumbledore "pleading for his life" is too strong. There's no way Rowling would ever make him do that. Snape is good, has to be good. Don't fret, Eliza!
But that begs the question - of what good is it that he's good? What can he possibly do for the good side if he's
this deep under cover? He better have one hell of a redeeming moment in the last book. I'm thinking he may very well die to save Harry, in order for Harry to do away with Voldemort. Something like that.
As for Dumbledore being really dead...I think he is really dead. It took me a few books to accept that Harry's parents weren't coming back from the dead, and Rowling has always said that death is death. But he may show up as an Obi-Wan to Harry's Luke, somehow. Perhaps just through saved up Penseive memories. There's no way he's just going to go out and start finding Horcruxes, never mind destroying them, which we have no clue how to do.
Disneyfan mentions above that he was very sad about the fabulous threesome not going back to Hogwarts next year. When I read that, I was extremely excited! It's about time they had to stop worrying about classes and exams and got the hell out there to fight evil head on. Sweet. I hope the next book is excitement from cover to cover.
Other basic notes - I really liked this one. It dragged a bit for me about 1/3rd of the way through. Nothing was happening, really. The built up tension was awesome by the end though, as usual. I was reminded of the wonderfully long climax in PoA, one of my favorite parts of the whole series.
As a writer myself I was very impressed by how she introduces everything all over again and in a fresh way, and reminds us of things as we go along. Her characters are still amazingly realistic (almost frighteningly so!) and I was once again reminded that there is a reason these books are revered, even though I don't revere them nearly as much as many others do....she's very, very talented.
My one problem with her is this. Someone mentions an unfamiliar term and Harry thinks, didn't Snape mention that before? Oh yeah, this is the
exact sentence that Snape said, one time, 5 years ago.
Even a kid will see how dumb that is, and like Eliza pointed out, these are no longer kid's books anyway.