I just posted to the Boston board about Americans not observing European etiquette regarding sidewalk cafes, namely, that during busy meal times, it's not appropriate to linger at an outdoor table. People sit down, eat, and get out: there's a tacit understanding that it's rude to hog your table at such times.
I quickly got an objection: "Wrong! Europeans linger far longer than Americans do." Well, duh, certainly: indoors. Am I alone in having observed this behavior? I'm sure there are some differences in local customs, but I particularly have seen this etiquette observed in urban French cafes with outdoor seating.