A few years back when I interviewed for the position that I currently hold I was told by the HR Manager that the company has a business casual policy five days a week and that it was not necessary for me to come in wearing a suit.  I understood where she was coming from as I did not want to look to uptight compared to anyone else and she probably just wanted me to fit in.  I went against her advice though and wore the suit; I was clearly overdressed, and I did indeed feel a little out of place, but I got over it quickly as  I wanted them to know that I was serious about their organization.  I have no idea if what I wore even factored into their decision to make me an offer, but I was wondering what anyone's professional opinion might be on this topic in the event that I am presented with this situation again?

As a hiring manager I feel it is always better to be overdressed than underdressed.  If they tell you not to wear a suit - you could always go with the option of no jacket but with a dress shirt and tie, or no tie but a dress shirt and jacket. 

Always err on the side of overdressed as opposed to underdressted though!  Good choice in wearing a suit!

i would say that it's important to find the middle ground.

i completely agree that it is always better to err on the side of being over dressed. the fact of the matter is, everyone has a bias to offer respect and presume authority to those who are dressed in a traditionally professional manner. look at it like this...

say you're heading to some business and you need to speak with the top level person. you walk in and there are two people standing there. one is dressed in a suit and the other is in a polo-shirt and kakis. who's in charge?

...that's the bias to which i'm referring. as much as many people hate admit it, everyone subconsciously presumes credibility, power, and respect based on attire. if you have the ability to use this prejudice to your advantage, why not take it?

however, the other side of this issue is like this:
the person whom you're meeting may potentially be both your boss and coworker. if they make the effort to give you specific instructions to dress a certain way, it is reasonable to consider actually dressing that way.  your future boss just gave you an instruction. do you really want to start off by symbolically stating that your think his or her views are misguided?

also, this manner of dress is presumably the organizations dress code. and again, presumably, this dress code was adopted as a courtesy and benefit to the employees. this is part of their company "culture". to reject this dress code is reject their "culture".

so, i repeat, find the middle ground. perhaps, leave the tie at home and carry your jacket over your arm...something like that.