For the first time in my life, I looked at America from a British perspective. I noticed what Americans probably don't usually notice and what I never really did so much growing up.
On the shuttle in Dulles International Airport, Washington D.C., I noticed chatter. Everyone was talking, laughing, making noise, most of them smiling. On public transport in London, people typically don't talk unless they are on the phone, and they generally keep to themselves.
Americans are more outgoing, louder, striking up conversations with strangers, greeting people in shops, smiling as they pass on the street. Londoners live in closer conditions and seem to value the little space and privacy they have. I don't think the English reserve has as much to do with overall friendliness as it does with having more privacy and space in America.
One very obvious difference is obesity and too much skin. Americans are much bigger on average and seem to show more skin than Londoners. It may be because of the larger portions, attitudes toward food, and the weather. I'm not analyzing, just observing.
Tax. Londoners pay more tax, but it's included in the price. In New York, the tax is tacked on as a little surprise at the register. I knew this, obviously, but just how annoying that is became a lot more apparent.
Granted Buffalo and London can not be compared side by side and I'm not in New York City, which could be compared more easily with London, but these are a few differences I never really would have thought twice about before moving to London and coming back with that point of view.