I agree with the rationale stated in this article:

The Google OS Is Doomed

The only reason that Google is creating the OS is to screw with Microsoft.  Now if that is the intended goal then all’s well.  But to think that the Google OS is going to garner any significant market share is just naive.

For one thing, targeting the netbook space as the niche for this OS is going to be an uphill battle.  MS just spent the last two years crushing Linux in that arena and securing over 90% of the market for its own.

Couple that with the fact that linux netbooks have a high return rate –> Netbook returns blamed on Linux 'teething problems'

And couple that with the fact that the Google OS is going to be essentially a linux distro with a browser as shell and the future does not look bright.

Google will be lucky to get more than 5% of the netbook space, I’d be very surprised if it got more than 10%.  Which means a flyspeck of the market.  It will anger MS and make them work harder to get Win7 on netbooks, which is a good result in the long run, but nothing more.