One of the more famous differences - and one that took a great deal of adjustment, following my transition across The Pond - was the formatting of dates. My whole life, I was used to writing the date as dd/mm/yy. In fact, I used to take particular satisfaction from this format, because it meant my birthday - 18/11/81 - was a numerical palindrome (the same backwards as forwards).
However, this wonderful Laurence factoid has been turned on its head since I relocated to Indiana. Not only that, but it has taken me the better part of 5 years to break the habit of writing it the British way - a source of some embarrassment when dating checks. My landlord was, needless to say, unaware that there were 31 months in the year!
Speaking of years, one small but, nonetheless, noteworthy difference is that Americans tend to remove and when pronouncing the year (e.g. Two-Thousand-One, instead of Two-Thousand-And-One). While this variance is by no means as significant as date formatting, the British way is still prone to the odd (sometimes very odd) look from Americans.
Moreover, there are various nuances when it comes to simply telling the time. A quarter past four, for example, becomes a quarter after four, while a quarter to four sometimes becomes a quarter of four. Additionally, Americans are not as prone to saying half past four, and will never be heard using the abbreviated version half four, with four-thirty being the simple, preferred usage stateside.
Meanwhile, in the world of mathematics (or should I say math?), there exist differences that most of us probably wouldn't even notice. Decimals such as 0.2 are often pronounced simply as point-two, or occasionally zero-point-two, instead of naught-point-two. This is largely because the word naught is not in recognized usage in the States. On the subject of fractions, Americans will sometimes say one fourth, as opposed to one quarter, perhaps to distinguish it from a certain 25-cent coin.
Actually coins are another way in which numbers differ. The only coins that exist in wide circulation in the U.S. are nickels (5 cents), dimes (10 cents) and quarters (25 cents). In the UK, the average pocket is often weighed down by any combination of the 1-pence, 2-pence, 5-pence, 10-pence, 20-pence, 50-pence, 1-pound, and/or 2-pound coins. The last three of these are each heavier and bulkier than any of the American coins, which are refreshingly light.
Of course, weight - and measurements in general - is a source of much disparity. Remarking at my own weight some months after moving here (I immediately had to contend with Thanksgiving and Christmas), my brother-in-law asked me what I had meant by stone. For the uninitiated, a stone is precisely equal to 14 pounds. Similarly, when citing my height, Americans sometimes feel the need to correct me when I say six-foot-one, as opposed to six-feet-one, though the former is not altogether absent from the American vernacular.
In the world of sports, which throws up an almost endless stream of differences, numbers are employed in notable contrast between the two countries. You're not likely to ever hear, for example, an NFL commentator announce a three-nil scoreline, largely because the word nil, like naught, is not in use in the USA. Furthermore, a game/match that ends in a draw would be declared a tie.
Perhaps one of the most marked differences, however, is the way Brits and Americans format house and telephone numbers. For their part, the British like to make the former as much of a mouthful as humanly possible; 219 St. John Street would read two-hundred-and-nineteen St. John Street, whereas the Americans would simply say two-one-nine St. John Street.
Meanwhile, British phone numbers are typically comprised of eleven digits (including dialing code), whereas American numbers have only ten (including area code). Moreover, Brits very rarely say zero (if applicable) when reading a phone number, opting instead for oh (e.g. five-oh-seven-nine-oh-nine-three-seven-one).