First, as foodpillsyes points out in the comments to your post, there's a dedicated jailbreak switch on the first official Chrome OS notebook, which doesn't sound very walled-garden-y to me.
Second, I really like the sound of a cloud notebook, especially since Google announced that they're going to partner with Verizon for a 100 MB 3G data "whispernet" for all Chrome OS computers to ensure near-constant connection. (And certain "web" apps, like Google Docs, can function perfectly fine without any web connection at all.) I can't really imagine a browser OS replacing my desktop computer because I'm old-fashioned, and I like having my mp3s and other files in a physical location that is accessible to me, but I could imagine a browser OS being all I need for a portable laptop. It's basically like Google says: When I start working in the morning, I open a web browser. And that browser stays open until I shut the computer down at the end of the day. And then I go home and open a browser on my home computer and that browser stays open until I shut that computer down. While it's true that I use a lot of Word files out of habit, I could just as easily do that from Google Docs. Besides iTunes, I really don't use any other desktop files in the course of an average day. That sounds like cloud computing to me.
And while it's true that I could use something like the Jolibook if I wanted a non-Google-specific cloud OS, the fact is, I use Google a lot: Gmail, Google Calendar, Google Docs, and almost every other Google product. Making Google into my OS makes sense for convenience's sake. (And having a dedicated non-Chrome computer at home for backup in case of a Google disaster makes sense, too.) Granted, as dozens of commenters will eagerly point out, I am not a thoroughly educated tech guy. I use computers, and I follow all the gadget news, but I do not know how to code and I'm not from a tech background. I am a heavy computer user, though, and for my work and leisure time, I generally only need my computer to do 7 or 8 tasks quickly and efficiently. If I can get that use out of a simple OS that comes with lightweight hardware, why wouldn't I use it?
I admit it; all I want for Christmas is one of those Cr-48 Chrome OS prototype laptops. I am not ashamed to say it. Dear Google: Send me a Cr-48. I'll document the whole Chrome OS experience here on Slog, and I'll use the fuck out of that laptop.
