It depends on the industry. At one job interview I dressed up, which was a dress shirt, tie, and wool slacks. The first thing my first interviewer (who became my long-term manager) did was ask me to take my tie off. The interview uniform in my industry is generally going to be men in a polo shirt and khakis, although it might not even be that critical. Not sure what it is for women. That being said, the clothing choices of people who have interviewed me has varied. I've been interviewed by someone wearing a T-shirt and shorts. Someone wearing a suit might even be seen as trying too hard. Heck - the craziest thing I've seen is someone wearing a tie-die T-shirt, shorts, and with a long Hare Krishna style ponytail. He didn't interview me, but it was at a mass interview event, and I found out that he was an MIT grad.