The OS is the browser. That's pretty much all there is to it. When you turn it on, there's no desktop, no file system, nothing. It just brings you straight into a browser. They have webapps and games, but to do anything, you have to be connected online. There are offline apps, but their functionality is limited, because the entire OS is a beefed up Chrome OS browser, that's it. Unless you're prepared to do some serious hacking and flashing of the hardware, then you won't even be saving anything to the puny HDD the system has.
This OS is meant to be cheap, portable, and extremely fast, which means that when released they'll have small SSDs and no disc drives. There's absolutely no reason for one of these systems to have a disc drive, as you wouldn't even be able to access it through the OS without putting through some hacks.
So far, I love the OS and the system. I'm thinking about using it as a dedicated writing machine. The keyboard is amazing and feels so natural to use. The touchpad is a little quirky, but once you get used to it, it's not too bad. Love the fact that it's cloud-based, and I can save something, walk to any computer in the house, and retrieve it. Google really has something here, and I wouldn't be surprised if this were the future of portable computing, and not tablets.