I'm writing this from a CR-48 (Google's prototype chromebook). It used to run Chrome OS, but I uninstalled it in favor of Windows 8 due to one major problem: speed. For some reason, Chrome OS performance was really bad. Of course, this may have just been because the CR-48 was running a special version of Chrome OS. If the version on the actual chromebooks is faster, I wouldn't say that it's too bad of an idea to buy one. The OS itself is not too bad, and if you use Google Docs like I do, it's not too hard to get used to. Chrome OS has its fair share of problems, however; it doesn't naturally support java yet, so you can't play games like Minecraft or Runescape without trying to manually hack java on it. Also, it doesn't yet support Google Earth.
P.S. It's funny seeing a chromebook ad under your post.