Mulling over last week's not-very-momentous pre-announcement of Google's Chrome OS, it seems like the biggest question is whether Windows will run on the ARM processor, which will start appearing in the next generation of netbooks. If not, and Chrome works pretty well on ARM netbooks, this makes some sense.
But in general, in 2009 people don't have to wonder whether or not a cheap computer (potentially with very long battery life) that only runs web apps is something that they'd like to use. If you need Photoshop or Word, you should already be aware of that fact. If you're spending all of your time in the browser already, you know that.