Most of the time, I don't even realize the difference when I'm reading. In the beginning, when I read novels published in Britain, I did notice the extra u's and s's that aren't present in American english. Then I got online, and started talking to people everywhere in the world, and the different spellings became common place. I haven't started using the extra u's in my own typing yet, but I've switched from "theater" to "theatre" because it looks more sophisticated to me.
