I am watching the live Chrome OS Webcast
For end users, Chrome OS is a great idea - I would argue that most of my friends and relatives would be better off not running Windows, OS X, or (full) Linux.
What about software developers: still useful, but not a replacement for a laptop. In a pinch, assuming a terminal window to run remote bash shells, Emacs, etc., I could still get work done while travelling. Still, for me, a MacBook with Ubuntu and OS X with RubyMine, IntelliJ, Eclipse, OmniGraffle, etc. is just about perfect for my workflow.
That said, I will buy a Chrome OS netbook when they are available.