The question of the custom of kissing aside, I actually wouldn't be that surprised if the basic humanoid form wasn't fairly common elsewhere in the universe. After all, form follows function and function is limited by form. Dolphins, for example, could be 1000 X's more intelligent than humans but would never have a technologically based society because their form doesn't allow easy manipulation of their environment. They will never be space-travelers without the help of someone or something with arms and legs and fingers.
Too many appendages becomes redundant, too few and the ability to function is limited. The octopus is a very intelligent creature and can, better than a lot of creatures, manipulate it's environment well but it's ability to manipulate with precision is limited and they can't survive long outside of the water though. We have no examples of tentacled land-creatures so it's hard to guess how well such a species might do, even if intelligent.
Without the appendages for fine, detailed precision work, you'd have no industrial or technologically based societies. Without limbs for movement in an open (ie non water) environment, the creatures can't get around. Four limbs and bipedal seems a balanced yet minimalist approach to form. Any more limbs becomes redundant and any fewer, activity becomes limited.
I expect that many forms are possible for life, including some truely unexpected ones, even in intelligent creatures. But if we are ever to meet aliens who function as we do, with technology and societies and buildings of cities and space-travel, they're probably going to be more like us in basic form than they will be different.
