It depends...
When I see a coder wearing shirt and tie, all I think is that he's another modestly skilled type who couldn't cut it in the arena with the talented coders.
It does depend on context, though. In the office i'm usually in polo + slacks, but we have no formal code. Others are in shorts & t-shirts, some in more formal shirts.
All the same, if I'm presenting to senior execs I will put a dress shirt on (no tie) and if visiting customers as the "expert engineer you asked for" I'l pitch my code to what they're likely to expect. US customers outside of the finance world it'll be formal shirt and smart trousers. For finance I'll add a tie, for UK customers of almost all sorts I'll get the suit out. The days we're reorganizing the lab or having a BBQ it'll be jeans and an old company t-shirt that I can trash afterwards if necessary.
Of course, it helps that I actually like the chance to dress smartly and wear suit & tie, so I feel quite comfortable doing so. If only I could persuade my colleagues that black tie dinners can be fun :)
Biting the hand that feeds IT
