Windows has Office, Photoshop, web browsing and email, and a huge pile of big-name games from big-name vendors.
MacOS has Office, Photoshop, web browsing and email, Final Cut Studio, and a (very, very) few of the big-name games from the big-name vendors.
Linux (Ubuntu, Chrome, etc) has OpenOffice, web browsing and email.
Not intentionally trolling here, but the fact is that not everybody is a web or software developer. Every modern OS has a basic suite of internet access and media playback apps, but the fact is that people buy windows machines for a few reasons - it's What They Know, They Don't Know Any Better, and Their Game Or Application Doesn't Run On Anything Else* being the most common.
Bottom line, if all you need is a browser, a mail client, media software and a text editor... you can be OS Agnostic. You can choose whatever works best for you. Chrome could work for you as well as Mac OS X or Ubuntu or whatever.
If you're a gamer, a graphic artist, or do any sort of 3d modeling, Linux isn't on the table... and neither is the idea of running your application in a web browser.
From what I've read, I'd be able to do with Chrome what I can do with every other current OS on the market. And there's a LOT I won't be able to do with it.
So. What's the killer app? What compelling reason is there to use Chrome when everything out there already does web and email while giving me productivity ability that still doesn't exist on linux?
Disclaimer : I was seriously thinking on getting a netbook until I got my iPhone, at which point a netbook seemed pretty irrelevant. I was looking at Hackintoshing a Dell Mini 9, as the price is right and it would give me the applications I want to be able to use on the fly - stuff I can't do with the iPhone, but stuff I wouldn't be able to do with ChromeOS, either.
* File format tie-in is a big one here - I can't move to linux even if I wanted to thanks to my productivity hinging on (literally) hundreds of gigs of .psd and .max files. Switching to a 3d app that isn't Max or a pixel-pusher that isn't Photoshop would incur hundreds of hours of work cleaning up and retexturing models, environments and source documents for the new app, to say nothing of the learning curve.