The potential appeal of the Chrome notebook is its security-by-simplicity. If the only thing you can do is use Chromium, then your notebook is basically as secure as Chromium itself is (in theory, at least).
The irony is that we're essentially moving back to the way computers were a few decades ago - people used terminals to access a central computer. We moved to personal desktop computers for a while, then laptops (and mobile phones). It'll be interesting to see if the rise of interest in 'cloud computing' means that, in five years, our primary computers will just be portable terminals to access some main computer remotely.
Personally, I might be fine with that. Network speeds/reliability aside, everything I do could be accomplished easily over SSH, with X forwarding for a few applications. It's possible that these simple tools that we've had for decades could be packaged in a way that appeals to a more general use case.