I’m all over the place. Raised in Australia, i’ve lived in Canada and England, and i currently live in the US. I tend to “code switch,” often unintentionally, depending on whom i’m talking or writing to. For example, on this message board i use the term “asshole,” but on a UK-based message board that i frequent i tend to say “arsehole” (which is also the way i say it when i speak).
If i’m speculating about something to an American, i’ll probably say “i guess,” but if i’m talking to an Aussie i’ll more likely say “i suppose” (or even “i s’pose”).
Then there’s the whole range of single-word usage differences that i observe depending upon where i am and who i’m with.
Cookies or biscuits
Eggplant or aubergine
Fries or chips
Chips or crisps
Sidewalk or footpath
and so on, and on…
Also, when i called someone a “wanker” the other day on the SDMB, he asked who uses that term on “this side of the pond.” I also use “bloody” quite frequently, especially when i’m in company where “fucking” would be inappropriate, and where a proper adjective is insufficient.
As i said, all this switching is generally completely involuntary, although i will do it on purpose if i think it will make something clearer to the listener.