Here’s a list of some small and sometimes annoying things that need to be adjusted to in the US:
1. US spelling (e.g., “-ise” becomes “-ize”, “-our” becomes “-or”). US spelling actually makes a little bit more sense to me and some of the words are shorter by a character.
2. Lack of distinction in spelling between verbs and nouns (e.g., “become licensed by applying for a license”, “he practiced medicine in a private practice”). The US way is easier.
3. The lack of the metric system. Their scientists use the metric system, why can’t the rest of the country? This is my biggest bugbear, and I find myself having to switch GPS devices over to using meters and kilometers because I just don’t have any innate sense of how far away 800 feet or 1.3 miles is. And how much is 1 pint and 4 fl. oz.?!
4. Zealous use of periods (fullstops) to denote abbrevations (e.g., “Mrs.”, “U.S.”, “Sept.”, “Oct.”). However, the practice is unfortunately not uniform – lengthier acronyms and some two letter acronyms are not broken up with periods. Putting too many periods distracts when reading text. I prefer so-called “open-punctuation” which minimises periods. Using “S.&P.” for Standard & Poor’s is just messy.
5. Punctuation around quotation marks. US punctuation requires ending commas and periods to be placed inside the quotation marks. For example: That article made claims that were “bogus,” “inaccurate,” and “dangerous.” (As opposed to: The article made claims that were “bogus”, “inaccurate” and “dangerous”.) Also, Americans tend to put a comma before the “and” or “or” in a list of items.
6. “v.” in case names is pronounced “versus”, as opposed to “and”. The US way makes more sense to me.
7. Tipping and state taxes. Makes splitting a dinner bill among a group a herculean task.
8. Date formats (e.g., “October 19, 2008” instead of “19 October 2008”). The US system doesn’t make sense. When you use dd/mm/yy, you’re progressing from the most specific descriptor to the least specific descriptor, and you don’t need to add an extra comma when writing the long form of a date.
9. Different valedictions in letters and emails. “Best” seems to be the most common signoff in informal or semi-formal, emails around here (“Regards” seems to be the equivalent in Australia). “Sincerely” is used instead of “Yours sincerely” and “Very truly yours” is acceptable for legal opinion signoffs.
10. Differences in terminology. College and school instead of university. Pumpkins are for carving, squash are for eating. Shrimp are prawns. Etc, etc.
1:31pm (GMT -7.00) 
