I finally saw Up yesterday. I went to a 3d showing. The 3d was fun without being oppressive. People may have already told you about it, but I thought I was ready for the opening montage. I wasn't. One of the reviewers on CHUD described the montage as the most brilliant 20 minutes of cinema so far this century, so my expectations were pretty skewed, but goddam if I wasn't crying at the end of it.
It's hard to review a movie from a studio like Pixar without thinking about it in the context of all their previous offerings. If Cars was the Star Trek 5, Ratatouillie the Search for Spock (or even The Voyage Home), and Toy Story 2 (or The Incredibles) the Undiscovered Country, then Up is the Wrath of Khan. I think it will hold out against the future offerings simply because it all fits together so well. Nothing felt forced, nor was too much said. None of the characters was without humanity, and all were empathetic in some way, even the villain. I recommend this movie to anyone.