Up in the Air is smart and sexy and funny and very believable -- even with a rather daring plot twist toward the end. George Clooney plays a grown up, which bodes well for a long and graceful career (meaning he doesn't embarrass himself by wooing women half his age the way Jack Nicholson did).
Since so much of this movie is about downsizing, and what a profitable industry it can be for some, be sure you're emotionally prepared to see firings onscreen. Really. I imagine that if this movie came out a year ago, when I expected to be fired every other Monday, I wouldn't have enjoyed it as much.
On the other hand, watching it reinforces why when earlier in this decade, as three people who worked for me were let go, I'm glad I insisted on being there. There is a dignity to handling it correctly, and a kindness to letting employees vent their anger to your face. I believe it makes it easier for them to move on.