Like some others here, I followed Simon Conway Morris fairly well about convergent evolution. For land beings at least, aliens would need a form of locomotion and they would most likely need senses for light, sound, contact and most likely also smell and/or taste. I can't see any advantage to walking on more than two legs once you evolve beyond being a lump of meat holding itself off the ground, and once you have a good enough nervous system to handle balance on two limbs. Any but the smallest animals will most likely need active breathing of whatever counts for air on their planet, particularly with the energy needed to run a brain. I also can't see much advantage in having more than two ears or (despite my nickname) two eyes. These would need to be as close as possible to the brain and as far as possible off the ground for best coverage, and of course steerable to look/listen around. In other words a head at the top of the body.
Once Simon Conway Morris got onto the brain as antenna bit it seemed like a clear case of dualism. I think he may be suffering from the sort of cognitive dissonance that comes from trying to be honest to hard science and religion simultaneously (according to Wikipedia, SCM is a Christian who actively tries to reconcile science with religion, an unenviable task).
PS. Rebecca: your cycling problems aren't just due to driving on the left. In London we hunt down cyclists for sport.
