Moving to New Zealand twelve years ago and writing for government agencies, I had to adjust to British spellings of words. Writing for myself now, I switch back and forth depending on my audience and the setting of the book (somehow it seems right that a book set in the US is in American English, and one set in NZ is in British English). For my short stories, I often write separate UK and US versions if I'm sending them out to multiple places. Usually, I write with British spellings, and then use my spell checker set for American English to create the US version. I ended up doing the opposite today--using the spell checker to go from US to UK spellings--and discovered something truly horrible...BOTH -ize and -ise spellings (as in realise/realize) are officially acceptable in the UK! So the spell checker doesn't mark -ize spellings as wrong. Doing a little research I discovered that, in fact, the OED recommends the -ize spellings over -ise spellings (because -ise is apparently French). The problem is, I've never met anyone who accepts these spellings as British English. Ack! My spell checker is only half as useful as I thought it was!