The great thing about Google is that where others have failed, they have the power, money and market dominance to fail in a greater and more spectacular fashion.
Once there was Amazon, but Google took them on, with their power, minds and money, and they created something even greater. Of course, you've never heard of it because it was garbage, and was received about as well as a rat pie at a French-Canadian wedding. It was called Frugle, or Friegel or Froogle or something, but nobody can remember, and even attempts to 'Google' it come up empty.
Then there were other triumphs. With all their money, power, and market domination in the search sector, Google destroyed PayPal with their Google Checkout. It continues to be the fastest growing Internet checkout technology. Apparently, two people accidentally used it in 2008, eight people accidentally used it in 2009, over 100 people used it in 2010, and even more are expected to accidentally use it in 2011. The most common feedback on Google Checkout? "I thought I was using PayPal?"
For some reason, people think that just because Google is behind something, they're going to make it work. The sad fact is, when Google is behind something, they're probably going to make it fail.
The viability of Google OS as a threat on the desktop? It's lipstick on a Linux pig that's already been slaughtered and has started to smell. Technically, Chrome OS is undoubtedly great. As far as open source projects go, it's undoubtedly great as well. As far as helping the two or three people that want to 'print in the cloud' goes, it's probably perfect. Will it ever get an install base beyond a few techies that want to play around with something cool when they get bored at the end of their two weeks of holidays? That's highly unlikely.