Chrome loads fast, is spiffy and always up-to-date, so you don't have to deal with managing updates or synchronizing data. Some of your applications store data locally and you can use them even when you don't have an Internet connection. You're running 3D applications, portable software, music players, photo editors, development environments inside your browser. Google Chrome OS is a challenge: are browsers and web applications mature enough to replace traditional software?
By the time the operating system is released, Chrome will integrate plug-ins like Native Client and o3d, while Google Docs will already become the place that gathers all the files stored in Google's services. Chrome OS won't bring anything that's not yet possible on your current operating system, it will force you to change your mindset and make the operating system irrelevant.
Google Chrome OS won't be a traditional operating system, it will just be a wrapper for the cloud.
Now let's re-read Google's announcement from July:
"Speed, simplicity and security are the key aspects of Google Chrome OS. We're designing the OS to be fast and lightweight, to start up and get you onto the web in a few seconds. The user interface is minimal to stay out of your way, and most of the user experience takes place on the web. (...) The software architecture is simple — Google Chrome running within a new windowing system on top of a Linux kernel. For application developers, the web is the platform. (...) People want to get to their email instantly, without wasting time waiting for their computers to boot and browsers to start up. They want their computers to always run as fast as when they first bought them. They want their data to be accessible to them wherever they are and not have to worry about losing their computer or forgetting to back up files."
The clues about Chrome OS aren't very exciting probably because the operating system wants to negate its own existence and become invisible.