2. Save the suit for weddings and funerals. Seriously, wearing a suit to a programming job interview will actually knock you down a bit. In most places, there will be some concern that you will not fit in, especially if (as is common) there will be peers among the interviewers. Strike some happy medium between a suit and shorts and sandals.
That's not particularly good advice. Do some due diligence on the company you are applying to, if it is a financial services firm, insurance or some other highly conservative field then the suit should not harm you at all and not wearing one might be a huge detraction. I have 3 options for interviews: Suit, Jacket no tie, business casual. Never make the assumption because the work environment is super casual you should come in for a interview in cutoffs and flip flops.
The poster is right though that fitting in to the environment is critical. Only 11% of people that get relieved of their position in the first 12 months are let go for lack of technical skills, the rest is because they did not fit it with the companies culture or play nice in the sand box.
However, I can tell you, from experience in being on both ends of the interview gun that those conducting the interview will be able to tell within a few minutes if you'll fit in. How someone dresses is less of a concern to me than how well they can do the job and get along with others.
Here's a few other tips: If this is the technical interview, where the head of the department and a few of his team members are there prepare for the team members to throw out obscure programming references which you will probably never heard of or use. This doesn't mean people will do it but my experience is that some people take this as an opportunity to show off in front of the boss. Just be expectant of that. When you get one of those questions don't panic and don't be afraid to say you don't know. It's how you handle not knowing something that is more revealing...one of the things I loved doing was throwing it back at Johnny Smartpants, something like, "I've never heard of that or worked with it but that sounds pretty interesting, could you explain it?" Half the time what they were talking of I had done but we called it something different.
Be enthusiastic. And know their company. If it is not a software development firm accept that you are a cost to the company and your clients are going to be all internal. Your not there to be some smart ass programmer with a God attitude but to help the folks in sales/marketing/some other business unit/ get their job done. (Yeah, we're smarter, just keep that attitude on the inside ; ) ).