This thread struck a nerve -- the first time my team leader and I visited Honolulu to meet folks in our office there, the manager made a point to tell us to be sure to wear socks. Apparently, that manager had sent people away who were dressed too casually for the office or appeared to be in more of a vacation mode.
My approach to dressing for work in the islands was fairly calculated. The first day, I would come to the office overdressed (sportcoat, slacks and a tie), and almost every time, someone in the office would pull me aside and tell me that it was OK to sport the Hawaii formal look (slacks, pressed and conservative Hawaiian shirt, socks, loafers). I always waited for the validation, though, before I dressed that way.