Height in combination with your weight *can* be a factor (IOW, tall and skinny...very subjective term... cyclists will lack high end power and the ability to ride the flats well), but it is not exclusively a factor, to an extent. I can't think of any top level cyclists that are taller than 6'3" or 6'4" .. eventually it just becomes too difficult to get all that mass up a hill, even if it's all muscle. On the flip side, I don't think anybody sees Paolo Bettini as any less of a threat because he is on the short side.
taller people are (generally) at a disadvantage because they are more 'unaerodynamic'. In general the taller you are, the longer your legs. The longer your legs, the higher your seat and the greater your drag. i don't however, suggest that anyone takes a hacksaw to their legs or rides a bike several sizes too small...!