I have never been a fan of dress codes: there's no empirical evidence it leads to higher levels of performance (after all, not a single study on high performance organizations shows a correlation between performance and dress codes).
Furthermore, I am in total agreement with the philosophy of Ricardo Semler, as outlined in his wonderful article, Managing Without Managers. He speaks eloquently to the "rule of common sense" and notes:
“…we replaced all the nitpicking regulations with the rule of common sense and put our employees in the demanding position of using their own judgement.
“We have no dress code, for example. The idea that personal appearance is important in a job – any job – is baloney…A company that needs business suits to prove its seriousness probably lacks more meaningful proof.”