Danny O'Brien (an expat Brit living in the States) wrote an excellent Thanksgiving Day blog entry about sincerity, which really struck a chord.  I can't find any one bit to quote here, so I just implore you to go read it for yourselves.  It's funny because it's true - Jocelyn still doesn't quite get when I'm making dumb jokes, and I still don't recognise these different forms of sincerity that Americans have, let alone hold any hope of actually emulating them.