Some things I find interesting about Chrome OS, even if I don't end up using it myself:
1. Web apps are a plus for a secondary device, because you won't need to copy files back and forth, or install sync/VCS software (a hassle for non-expert users). HTML5/Gears storage remove some of the disadvantages by letting you continue work offline. (On the other hand, services like Dropbox have made it just about easy enough for non-expert users to do this with traditional "local" files.)
2. No user-installed native code means certain security concerns could be greatly reduced. All installed code is signed, verified on boot, mounted on a read-only partition, and can be restored to a pristine state by the firmware. Web apps are subject to browser same-origin policies and to Chrome's process isolation. Downloaded native code can run only in the NaCl sandbox. A broken app can't trash all your stuff, because data from each web site is accessible only to that site. (On the other hand, web apps are almost universally vulnerable to XSS and XSRF and to server-side exploits. NaCL has been broken before and will be broken again. The web security model is a start, but it has flaws both in design and in practice.)
3. The interface is simplified in a few key ways. Instead of windows that represent documents within apps and often have their own separate tabs or pages, everything the user interacts with is a tab within a browser. Not a big deal for savvy computer users, but for novices this is one less concept to learn. Everything is a web page; they don't need to be "installed"; they all appear in the tab strip and have addresses that can be bookmarked and emailed. (On the other hand, web apps share only the most basic UI conventions; they are often radically inconsistent from one to the next.)
4. The Chrome team's obsession with speed may prove to be one of those subtle, hard-to-explain benefits. (Like trying to explain why Apple's obsession with detail matters, to someone who hasn't used their products.) I never had a problem with Firefox until I used Chrome for a few days; now any other browser seems painfully unresponsive. Same thing with git compared to darcs/bzr/svn. When more operations move from "fast" to "instantaneous" it changes the feel of the product, and that affects usage patterns.
5. Compared to Windows, Mac OS X, or normal GNU/Linux distros, Chrome OS has less overall code, is conceptually simpler, and has few legacy/compatibility constraints. If it's managed right, this could mean that it will be faster to evolve and optimize, easier to secure, and ideal for experimenting with new technologies and user interfaces. It will also help motivate next-generation web applications and web standards.