I'm a Yank who's been living in the UK (yes, Yorkshire -- how did you guess?) for 7-8 years now, and I'm still running into unfamiliar words -- although not as often as I did when I first moved here.

"Stop" was one source of misunderstanding for me; at work one day, someone asked me if I was "stopping". It was after 5 pm, and I said yes, as I expected to stop working soon. However, his use of "stopping" meant "Are you staying late?" -- as in "stopping in" or "stopping by". I guess I should have said I'd only be stopping while a little while longer!

"Nesh" is a great Yorkshire word, used to describe someone who wears a jumper/sweater or coat when everyone else is in t-shirts (i.e. someone more susceptible to cold than most).

For those interested, the English to English Dictionary thread has many more examples, including a parody I wrote on the subject, titled Don't Know the Words... (for My Favo(u)rite Things).

Cheers!