American here. Yes, we are very, very different. Our path with the UK diverged a long time ago. Based on my experiences I think Americans are more optimistic, louder, more open to new people and experiences, less interested in foreigners and foreign countries, more casual, and definitely less inclined to talk about details of our sex lives with people we don't know very, very well. We also don't talk about money with people we don't know very well. I'm constantly amazed at how much MNers know about the finances of their friends, family, and acquaintances.
I think Brits are more polite, more formal, less brash and less optimistic than Americans. And I'm not trying to offend, really, but you think that we think about you a lot more than we do. Most Americans hardly ever think about the rest of the world unless something big happens out there.
Not to say that we don't keep up on world events, we do, but we don't really worry much about what the rest of the world thinks, feels, etc. I guess I'm saying that we're aware, we're just not that influenced. We're too big, too dynamic, and there's always so much going on here in science, tech, the arts, we're always moving, growing, changing in a way that I never saw or maybe just never noticed, when I lived in Europe.