It depends. For netbooks this would probably be nice because it boots fairly quickly and is just a web browser.
For any other purposes, I don't think it'll be very good. Only use I can think of is a way to really quickly access the internet but you'd still want another OS that can do more.
The thing is Google is working to reimplement all software as web services, so that you don't need a full OS, i.e. turn your pc into a light client, with the browser as your work environment. Look at Google Docs for example. The reason Google implemented their own Javascript engine in Chromium/Chrome is to have a good platform for running their services.
Also, BTW: this isn't the ready product. You might want to read
this. Google are simply following the bazaar model of Open Source software development, where one mantra is "release early, release often" -- this is the first opening up of deelopment, which means a lot will still happen. I wouldn't be surprised if something powerful comes out at the end.
On a side note, I find it rather curious how with Chrome OS, despite its basing on Linux, isn't jsut called Linux, whereas with other systems such as GNU/Linux, people call it Linux (despite that being only the Kernel, i.e. 1% of the code). Just shows how some people don't have too much of a clue of what's what.
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