i09 has this great article about different perceptions an alien race might have, just touching the surface in terms of sight, hearing and smell. It's fascinating to think of the things that might be different, and what kind of stories this might cause. Indeed, I have seen some trace of this in Larry Niven's "Outsiders" race, who do not exist at the same speed as humans, and also in China Mieville's Hosts, who are unaware of language as used by humans.
