Vista ships out of the box with some simple yet helpful features if you travel to locations in different timezones. My favorite is a new feature of the Taskbar clock.
When hovering over the clock in the right hand corner of the Vista Taskbar a customizable little tooltip pops up, showing the current time and date and additional timezones. The zones and display names are configurable.
The settings dialog is available via Control Panel or the previously shown window. Here you can add additional clocks/times so you always know when you are in a foreign country in a totally different time, why you can't sleep.
Of course you could have used the Windows Vista Sidebar to display many additional clocks but using the Taskbar clock seems more convenient and less obtrusive.