As a Canadian, I grew up speaking, reading and writing English as my primary language and French as a secondary language (mandated in our school system). Canadian English is based on the original British English but heavily influenced by our great neighbours to the south, America.
American English and British English sound the same (excluding regional accents, of course!) but there are many words which are spelled differently, such as "neighbour" and "neighbor". Some other words which Canadian and British (and, most likely Australian, New Zealand and other former colonies of Great Britain) spell differently from our American cousins are:
British Spelling American Spelling
The list goes on, but you get the idea, English can be confusing! Living in Canada, our media (TV, movies, etc.) are heavily influenced by America so we are exposed to various spellings of common words from a young age. While the words sound the same when spoken, they look very different when written which often causes a reader to declare that a word has been spelled incorrectly, even though it has not; the writer has only chosen to use either a British or an American spelling.
In my full-time, non-writing career, I deal with an international group of people, including many Americans. Whenever possible I try to adjust the spelling of my words so that the recipient of my correspondence is not distracted by what they may consider to be "incorrect" spelling. The same holds true with my novels.
When I published my first novel, Bloodlines: Cove Point Manor, I received a couple of quasi-negative comments about spelling errors. There were a couple of errors that slipped through, but not to the degree that the reviewer commented about. With further research I discovered that the reviewer was an American and made the assumption that the words were misspelled as they were written in British English, not American English. I had a similar comment made to me on my second novel when I made the decision to write in American English, only this time the criticism was from a British reader.
As a Canadian, I am accustomed to seeing different spellings of words, whether they be in British English or American English. Either form is acceptable to me, and if I am reading a book or article by an American author, I expect to see American English. The same holds true for a Canadian or British author. The spelling does not distract me unless I start seeing a mixture of American and British spellings being used.
My largest reader based is in America, so I have made the decision to spell my words using American English rather than Canadian or British English. Sometimes I still slip up and spell a word using British English, but with my spell check program set on American English, most of the words are caught and corrected. I will still, undoubtedly, receive comments about incorrect spelling of words (nobody is perfect!), especially from my Canadian and British friends, but I am targeting my books to my market, and at the moment my largest readership is based in America.
Oh well, you can't please everyone!