Disclaimer: this is not an official answer from Google, and while I have worked there I do not at present.

There are data centers around the world, however Google only stores sensitive data in locations where it can guarantee security and privacy[1]. Quoting from an official blog post from 2006,

"Protection of user privacy -- We will not maintain on Chinese soil any services, like email, that involve personal or confidential data. This means that we will not, for example, host Gmail or Blogger, our email and blogging tools, in China."

What this means is that your data could be stored in a number of countries, which will include a copy in the U.S. and not include a copy in China.

[1] http://googleblog.blogspot.com/2006/02/testimony-internet-in...

It hopefully won't matter. I'm on the mainland, and my gmail, igoogle (now re-directed to google.hk), and google translate are up.

News and search have been surgically removed.

edit: search is up? down? wtf? Whatever, I can use yahoo.