I have to admit, when I read TS (or any other "American" show) and the spelling is not American, I am temporarily thrown out of the story. When I read dS, HL, etc, I skim right by the spelling if it's "British." I actually use a Canadian beta for dS to make sure Fraser doesn't do/say anything too USA. (In return, she has me look over her American stuff to catch Canadian spelling and wording.)

Just my two cents, worth nothing. ;>