I think if you can remove your ego from the equation (I don't think anyway likes being told they're wrong or what they've done is stupid/illogical/inefficient), they're an excellent way to learn new approaches and how other people think about code. Sometimes a good excuse for vocal devs to soapbox and assert dominance too in these lovely open-plan devpits.

That said, most times I've had code reviews, it's more of a superficial rubber stamp. Probably been guilty of doing that too... not really as much fun reviewing code as writing it.