I know of several of my friends who have interviewed with Microsoft in Redmond WA in jeans and tees...all of whom were extended offers of employment.

Of course, the opposite can be true: I interviewed with them this past March in business attire and I did not receive an offer (but they did ask me to re-apply this September instead of traditionally waiting out a year: apparently I was a strong enough candidate to warrant a 6-month wait out).