http://www.youtube.com/watch?v=4KRZQQ_eICo&feature=player_detailpage#t=4919s
This video is great the whole way, but from 1:21:00 or so on is pertinent to the alien discussion.
Basically, he says that our dna is about 2% different from a chimp. Maybe our intelligence difference is also on the same scale. As smart as we think we are, maybe we're only 2% more intelligent than the chimps. The smartest chimp is about as intelligent as baby. Now imagine an alien that is another step up that scale. Smarter than the smartest human when just a baby. Then he makes the hilarious joke that maybe the reason we haven't been contacted is that aliens have visited earth and determined that there was no intelligent life.
edit:
Basically what I'm saying is that there's no reason to believe that a smart alien would look anything like us because there's no reason to believe we're actually that intelligent. We're intelligent on this planet, but that doesn't really mean anything on the grand scale of things.