Beginning with Chrome 11, Google's making some changes to the UA string, which can affect website compatibility. "When websites want to know what browser you're using, they often examine the "user agent", or "UA" string. This is a string that provides information about what browser and operating system you're using."
Here's the Chrome 10 UA string on a few different platforms:
Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US) AppleWebKit/534.16 (KHTML, like Gecko) Chrome/10.0.648.204 Safari/534.16
Mozilla/5.0 (X11; U; Linux x86_64; en-US) AppleWebKit/534.16 (KHTML, like Gecko) Chrome/10.0.648.204 Safari/534.16
And, here's the Chrome 11 UA strings on the same platforms:
Mozilla/5.0 (Windows NT 6.0; WOW64) AppleWebKit/534.24 (KHTML, like Gecko) Chrome/11.0.696.16 Safari/534.24
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/534.24 (KHTML, like Gecko) Chrome/11.0.696.16 Safari/534.24
So, why Google is making these changes? It's because "websites tend to use common pieces of code to check all browsers' UA strings, it's important for browsers to stay in sync with each other. Mozilla has made the above changes in Firefox 4, and we wanted to change Chrome to match as soon as possible, to minimize the disruption to web authors," Google reasons.
If you see problems sites you think might be caused by the new UA string, try running Chrome with alternate UA string using --user-agent="<Put older UA string here>" command line flag. (You can double-check the UA string Chrome sends to websites by typing about: in your address bar and hitting .) If that fixes the problem, you can report it in the bug tracker.
Here's the differences in detail: