I've worn slacks, a dress shirt and dress shoes everyday of my career in IT. I did so initially because I just enjoyed it, but I quickly realized that it helped add some initial credibility due to my age. I was in high-level positions in my early 20s, and every bit of a professional edge helps. Your clients/colleagues should be able to identify with you, and having an obvious disparity in professionalism makes that difficult. This goes the opposite way as well; people that dress in suits everyday when everyone else is in a simple dress shirt without a tie tend to annoy others.
Point: Don't stand out. That might sound conformist, and I know there are people that will always say, "Dress for the job you want", but overdressing can be just as bad as underdressing. It makes you look too eager, green, and in some cases might simply annoy people to the point where they don't wish to work with you. I've seen company directors at fortune 100 companies tell consultants to forget the tie or stay home.
One last point, I promise. Many years ago I worked with a consulting firm, and we were billing out at a very substantial rate. We had some consultants that would literally show up with holes in their pants. These people were very talented, but when a client is paying you a substantial rate they tend to want you to at least look like you can dress yourself. It's a bit of a paradox, really; clients don't likely appreciate paying substantial rates, but at the same time they want you to have a certain appearance, office, etc. There's a reason why so many of the major firms in the US have outstanding offices in the more prestigious cities in the more prestigious areas. It's all about perception.
I shop at two places for my work clothes: Banana Republic and Brooks Brothers. BR's dress shirts aren't of the best quality as they tend to look too casual; they're thin, they wrinkle too easily, and they simply don't look polished. Brooks Brothers has fantastic dress shirts, and they last forever. They always look clean and wrinkle-free (mine do at least). I buy my dress pants from BR simply because they have a better style and they're incredibly comfortable.
Hopefully this didn't come off as too superficial. It's the nature of the business. Play it or lose, imo.