It depends. Certainly a suit is never going to be helpful when interviewing at any true technology company, whether it be a startup or not. But the idea that it would hurt is situational: certainly if a mid-career professional walks into an interview in a $500 suit, his/her attire just screams "I've been writing VB code for 10 years in an IT department."

But if it's on a recent graduate, or an amateur trying to break into hacking as a profession, not so much. There, it's just a sign of naivete. It's cute, not dumb. It might be awkward, but at least it shows the candidate cares about the position.