I was raised on the 12-hour format (for example it's now 9:08PM), and that worked for me for a long time... then I got a job in security and was forced to learn 24-hour time. I liked it so much I converted as much as I could to 24-hour time. You can do it in Windows, though it's tricky... My watch would do it, but my alarm clocks, the microwave wouldn't. And most people don't understand 24-hour time, so you have to compensate for that.
I just think it makes more sense, though. Why does 12 come before 1 (12pm, then 1pm) and why do they start over halfway through the day? That's just stupid IMHO. And, what if something happens to slow the Earth down, so one rotation takes 25 hours? Will 12:30 be the new noon and midnight? I was thinking about this since on Star Trek: Deep Space Nine they have 26-hour days. 13th hour, indeed. But they use 24-hour (26-hour, really) time, so they're set up for it. And though DS9 is fantasy, when we move into space travel, we'll have to use a system more friendly to varying day lengths.
The difference in date formats is simpler. In America we would say today's date as December 17, 2005, but in the UK, they say 17 December 2005. In America we might say "The seventeenth of December" but we'd never write it that way. At first I thought it was crazy... and to an extent I still do. I do prefer the UK way, DD MMMM, but you have to use the word. 17/12/05 is OK, but only because 17 > 12. If the Day is less than 13 and not equal to the month, it's confusing... If I say 3/2/05, how do you know whether it's 3 February or March 2? (Of course 4/4/05 is April 4, regardless.) But, despite the confusion, I try to write the date UK-style, with the word for the month. It just makes more sense... you have 30 days in a month, 12 months in a year. Second - Minute - Hour - Day - Month - Year - Decade - Century... it just makes more sense to do Day/Month/Year. (Just don't ask me why we do Hour:Minute:Seconds because I know that's completely backwards, following the same logic.)
