Last Night

After slogging through “Atonement ’’ and wilting in “Never Let Me Go,’’ Keira Knightley needs a movie which doesn’t take itself so seriously that all you can do is laugh at it. “Last Night’’ might not take itself seriously enough. It’s a light, minor, eventually tedious movie about married Manhattan yuppies — Sam Worthington plays Knightley’s spouse — who spend one evening in separate cities feeling out their attraction to other people. It’s the sort of movie that thinks cutting between two different stories makes it art. Usually, it feels like an exercise in art. There’s a lot of calisthenics but very little beauty or truth or whatever it is the movie is going for.