http://www.timesonline.co.uk/printFr...35-523,00.html
I thought this was a pretty nifty article. Ganked form Neil Gaiman's blog, because he normally posts interesting articles.
I'm pretty sure my smile varies between the open mouthed and crow-eyed sincerity of the "British smile" and the upper-teeth exposed only because I'm self-conscious of how I look while smiliing "American smile".