Ack, just use English-English spelling Stoday! I would never dream of using American-English spelling just because it's a predominantly American site; it's a) too much hassle to think about spellings which I naturally spell correct anyway, b) part of who you are (if you visited America you wouldn't put on an American accent, would you?!) and c) very educational for our cousins across the pond (and can be amusing when you use common usage words here which they've never heard)!
Besides, I think that very few words are spelt differently; it's generally the meaning and pronunciation of certain words which may be different (see c above)!