Initially I thought that Chase had left the whole matter of whether Tony survives ambiguous. Now, after a half a day of thinking about, and a little bit of reading some of the blog theories, I believe it is actually less ambiguous than we all thought at first blush -- and more artful.
The keys to the thing are Bobby Bacala's comment in the first episode of the second half of the 6th season, "when it happens, you don't even hear it."
The final scene was mostly shot from Tony's perspective. Tony was watching the door. When the scene went black, that was Tony's viewpoint.
Remember, it went black for a considerable period of time (5 seconds or more, possibly: an eternity on TV).
Alessandra Stanley wrote a horrible review in the Times... she didn't get it at all. She said:
But Mr. Chase’s last joke was on his audience, not his characters. Tony, Carmela and A. J. are gathered at a diner in a rare moment of family content that cried out for violent interruption. A shifty-looking man walks in and eyes them from the counter, then, in a move echoing a scene from “The Godfather,†ominously enters the men’s room. Outside, Meadow is delayed, trying to parallel park, then begins walking toward the restaurant.