depends on a lot of things.
I spent my first bunch of years in the boston area and the east coast of the US is much more conservative than the west coast. I did wear jeans and sneakers and when it got hot, short pants and a tee shirt. most people wore button down shirts or polo style shirts which are a step up from a simple tee shirt.
when I moved to silicon valley, though, I found I was over-dressing

over time, I converted to wearing sandals and shorts most every day to work (the weather is nice here and people are much more casual, as well).
its also cultural. in my field (software) most of my co-workers are from india and china and korea. folks from other countries seem to not want to dress too casually. I've never once seen any of my foreign co-workers wear shorts and rarely do they even wear tee shirts.
for interviews, I will wear long pants (jeans) and a nice polo shirt, sometimes a company logo shirt (still polo style, with a collar). I will never ever ever wear a tie for work or for an interview. if I saw an engineer wear a tie for an interview, I'd think he was 'new around here' or was more of a management type person
