A design document posted at Google's Chromium development site suggests that a system for desktop notifications would allow Google Chrome to notify when downloads are done, web sites need one's attention, and let extension developers creatively grab attention.
There are no screencasts to ogle or experimental tests to try out, but it definitely looks like a system will be put in place to allow placing "toasts" on a user's screen when certain events happen. Interestingly, the documentation suggests that if the Growl system is installed on a Mac, and a Linux system is using DBus desktop notifications (a.k.a. libnotify), Chrome will route its notifications through those channels. No indication what will be implemented in Windows or non-Growl-ed Macs, but it's an intriguing signal of things to come.
Desktop Notifications [Chromium Developer Documentation via TechCrunch]