For my part, I wonder at those who can't be bothered to proofread or find someone to proofread, and then get upset when they get flamed. There are numerous threads in these forums with people volunteering to proofread; any one of us would be pleased to save everyone varying amounts of grief.
As far as British and American spelling, am I unusual in that I already knew about the differences? It seems very few Americans do, judging by the number of Brits and Canadians that have been stung on this one. I actually enjoy stories with British spellings and slang; one of my Harry Potter books is in the UK edition.(The measurements kind of throw me off, though. Damn metric system.)
Morrighan