var is_chrome = window.chrome;
The following string represents Chrome's full user agent:
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/525.13 (KHTML, like Gecko) Chrome/0.2.149.27 Safari/525.13
Have any Chrome-specific functionality you want to build? Maybe a MooTools slide-in script that says "Hey, you're using Google's new browser!" It's probably too soon to try to fix Chrome-related bugs, but knowing how to detect it sooner rather than later is a good thing.