I just got back from my first real UK golf trip. I think the walking and the indifference/welcoming of the weather are the two most obvious differences.
Aside from that, the biggest difference I saw was with the caddies... I'm a caddy and after playing 8 rounds at 5 different courses, I think one of the biggest cultural differences is the way the caddies are treated. First, they only get one bag at a time. This was the case at all of the courses. Two of the caddies in Scotland when asked how they came to their course, answered that they "loved being in customer relations".... Back here in the US, that idea of customer relations never even occurred to me, and not a single other caddy I have come in contact with here has answered that question like that. US caddies, from what I have seen, are there for the $$$, nothing more, nothing less. They feel that not only does it pay well, but its just a simple, easy way where they can make a buck without having to work to hard. Of course there are those, like myself and a few others at my club, that caddy because they love the game, they love to be outside and really get into the team aspect of the sport, but in general I found the UK caddies to be far more capable and infinitely happier with calling themselves a caddy.