Do you care about the small differences in spelling? (UK vs. US)

I care because I find it legitimately interesting how the English and American versions of the language have evolved in different directions, as have the Canadian and Australian languages. I don't care because I think "EVERYONE SHOULD SPEAK THE SAME LOLOLOL", but I care because it's interesting :P

Language is, in my opinion at least, at it's core a device to facilitate effective human communication. I care about how well language does that job, and I think simplifying it can sometimes aid but usually detriment language's ability to make communication effective. So I care in that regard too. I care that having a wide range of equally valid versions of one language can hinder communication when it happens on an international level, for example through the internet, but I don't know how to solve that problem without destroying culture (which is too high a price to pay) and hindering communication on a local level.

What I don't care about is whether someone says behaviour or behavior. So long as the people you're trying to communicate with can decode you I'm not bothered :)