It's a pretty good movie, but make sure you, and the people you're going to see it with, know it's a documentary. When I went to see it my companions thought it was everything from an animated feature to a movie about exploration in the antarctic (some of them actually fell asleep during it ...), the trailer is very misleading.
But once you get that sorted out it's definintally worth seeing. The filming is great, although some of the bits without narration do drag on.
Oh yeah, if you have a choice see the American version (instead of the european one). In the European version the penguins are meant to be the narrators, which makes it a quite bizarre movie.