They have done some psych studies showing that most interviews are decided visually in the first minute or so.
In my experience, that has been the case - if you get the interview, then they like you and it is yours to lose by saying stupid shit.
Although for the first time lately I have interviews and feel like I have had to justify why I am there, and it is a wholly unpleasant experience.
I have a thread up about it right now.