I've never felt my proportions were anything other than average (5'10", 160 lbs), but recently I had to buy a dress shirt and got fitted properly. The store employee was doubtful he could find anything for me as I have freakishly long arms and a thin neck (in terms of being fitted for an off-the-shelf dress shirt, anyway). I guess the thin neck comes from my line of work, pencil necks and all that.

Neal