If you're an avid traveller, you might want to think about picking up a soon-to-go-on-sale Doodad pay-as-you-go SIM card: it offers flat-rate, 3G data, around the world, and will work in any unlocked GSM device. Neat.
Flat-rate doesn't mean you get charged the same in every country, but you can at least set caps for yourself so that you always end up spending the same amount. You'll be stumping up 30 cents/MB in the USA, South Korea and Australia for instance, while prices jump to 60 cents /MB in China, Canada and the UK. In the most obscure countries—think British Virgin Islands, Haiti, Samoa—it costs $1.20/MB.
You also get a full year to use credit added to the account, so if you don't use it all on one trip you can roll it over to the next. Doodad is currently looking for volunteers to help launch the service in 54 counties around the world. If you're traveling in March, go fill in their form—and you could get $300 worth of data to use during your travels, as you see fit. [Doodad]