I've found two oddities with time-type settings in OS X (all versions thus far).
- Changing the time zone after install: I found that it won't stick. Here's what I now do (and it works for me on multiple systems, including when booted off a FireWire drive). Traverse to System Preferences -> Date & Time -> Time Zone -> Closest City:, then enter a major city in the timezone (Vancouver - Canada, in my case). It'll do completion as you type, so when you have a city in the correct time zone, press return or enter (without this, it's not saved). It should now "stick."
- Getting a sane date display format - YYYY-MM-DD: I found that this won't stick if you just change it for the U.S. region, so here's what I do. Traverse to System Preferences -> International -> Date and change the Region to U.K. then change the Short Date to Year-Month-Day, the Separator to "-" and check the Leading zero for day, Leading zero for month, and/or Show century (as desired). It should now "stick."