It's not a common thing in this country outside of the South, where they put a bit more emphasis on manners than here in the Northeast or out in Ohio. (I can't really vouch for the middle of the country, beyond the fact that the Southerners who worked for the Red Cross were very appreciative of me using 'sir' and 'ma'am' when we met on a flood relief operation in Wisconsin.)

I actually started using the 'u' spellings long before I got interested in Canada. Back in... mmm, high school, I think... I started adopting a number of British spellings because I'd read the James Herriot books once too often, and because I'd seen Chariots of Fire. I liked the little fillip of difference it gave my writing. I never adopted the changed spellings wholesale, but I've got just enough difference from American standard written English to stand out.