One of the best interviews I ever had came after I said to the recruiter (after the first round of interviews) "I don't think these guys are interested in me." The hiring manager scheduled another interview the next day and proceeded to take me through each lab, showing off all the cool stuff they did. That morning was quite clearly a "come work for us, it'll be fun" invitation and I appreciated it.

Now that I'm in the position to do hiring, I try to have the same attitude.