US spelling doesn't usually bother me. Another country is perfectly entitled to adopt its own linguistic conventions, even when they involve rearranging the spelling of our own tongue. I'm not even too worried about Americanisms entering UK usage. In fact, I remember Bill Bryson provising a list of words that aren't, but everyone thinks they are.
The issue that bugs me is this. In the New York Times recently, they have been reporting on British politics, and they repeatedly refer to the Labor Party. We all accept that Americans have colors, travelers, etc, but Labour Party is a proper name. It should be spelt exactly as the organisation (or is that organization?) spells it. In the same way, we shouldn't have Technicolour, as it is an American brand name.
I'd write to the NYT, but somehow, I don't think they'd be very interested!