Did you know that ~80% of the traffic on Google, Facebook and Twitter come from outside of the US?
Fred Wilson (avc.com) has written an insightful blog post titled "Does Rest Of World Matter More Than The US?". Fred believes that localization is key to monetize outside of the US:
The web sector needs to start working harder on international monetization. [...] Web services that are highly international today should invest in fully localizing their user experience and then start thinking about monetizing outside of the US.
This is the reason d'etre of web services like Transifex: the vast majority of international speakers, who can stay on your website twice as much and have 4x more chances of buying something, if your website speaks their native language.
Of course the US traffic can achieve (much) higher monetization than other countries in most industries, but the monetization does follow the high numbers of international visitors:
Even if international traffic could only be monetized 25% as well as US traffic, when your international traffic is 80% of your total traffic, you would make as much money internationally as domestically. So that's a lot of potential out there to be tapped.
An interesting comment was made by daveclark, mentioning that the cost of winning a local market shouldn't be underestimated. Businesses which 'inherently scale friction-free across markets' should 'game on', while others might need much more work than just localizing the user interface (think, for example, selling shoes or books). Lots of good comments on the article.