John Clayton is on the local ESPN station now, and he says it was definitely an interception. He says that Tate had the ball, but that Jennings had possession when he landed on Tate and therefore had control. His main criticism is the way the referees did not confer with each other and made contradictory calls.
I still think the right call was made, but I know I'm in the minority. On the other hand, bad calls happen. The Immaculate Reception was an illegal catch according to the rules of the day, but nobody cares about that anymore. Furthermore, the Packers could have ended the game by getting a first down on their last offensive series, or by knocking the Hail Mary to the ground instead of trying for the INT. The controversial call was notable for being the last play of the game, but it was not like the Packers played a perfect game that was stolen by dastardly officials.
EDIT: Clayton just called the play "The Inaccurate Reception." I wonder if it will catch on.