I bought a Chromebook (the Samsung ARM model) a couple of weeks ago. It became increasingly obvious that the battery situation on my beloved Thinkpad was going from bad to worse, and trustworthy replacements are hard to find--especially on a budget. I still have lots of uses for the Thinkpad (it may end up serving as a media center if the XBox dies again), but it can't really be portable the way I need it to be when my classes start back up again.
I don't particularly want to get into the question of whether the Chromebook is a good solution for other people. I'm not other people. I can't tell you whether they'll like it. I think it covers a great deal (if not all) of the average person's computer usage, most of which is spent in a browser, but I don't have evidence to back that up, and I'm not going to treat my case as representative. What I can say is how it's working for me so far, specifically as a writer and a web programmer with a heavy emphasis on Linux tools. And the answer is that, for the most part, it's working very well.
My top priority was battery life and portability. I'm on a bus for two hours a day, and one of my goals this year has been to turn that into productive time by working on my textbook, lesson plans, or other projects, preferably with some juice left over for when I get off the bus and walk into my classroom at night. The Chromebook definitely has that covered. I'm not sure the battery meter is 100% accurate, but I tend to run out of energy before it does, and the ultrabook size is easy to carry or slip into a small Timbuktu bag. The build quality seems solid, although I'm a bit uneasy with the idea of cheap, "disposable" laptops like this.
Second priority was a decent browser experience, since (like most people) I spend most of my time these days in a browser. Depending on the page, the Chromebook can be a little slow sometimes, but it handles most things the way you'd expect Chrome to do. It's easy to forget that it's basically a smartphone chip hooked up to a big screen. WebGL performance is surprisingly good: I loaded up the new Google Maps beta, and had no problems panning around a 3D textured version of downtown Seattle. Flash is built-in, so I'm not missing that (the new XBox Music site, like a lot of its competitors, still uses Flash for streaming audio). Tethering works flawlessly.
But my third priority (and still a must-have factor for me) was the ability to develop and write on the Chromebook itself. Being able to log into a server from the Chrome OS SSH client is fine, but a lot of the time I still don't have a network connection. If I can't work locally using the tools I'm used to, it's useless to me.
There's a thing called Crouton that installs a full, semi-sandboxed Linux distribution alongside Chrome OS. The two operating systems share a kernel, but have separate sets of binaries and processes. The result is a complete Ubuntu server stack that I can dip into whenever I need to work offline, including Git, NodeJS, PostgreSQL, and all the other command-line utilities I've gotten used to having. Crouton's totally supported, by the way: you need to be in developer mode, but that's just a keystroke away.
You can even set Crouton to run the graphical interface for the second OS, toggling between them, but considering how much I hate the Linux GUI situation, I haven't bothered. Chrome OS works nicely to manage my terminal and browser windows--the Aura interface that they've added lately does a decent impersonation of Windows 7, including an improved version of Aero Snap. There are some quirks--the dedicated "switch windows" button doesn't seem to quite work consistently--but it's already the best Linux window manager I've used.
The weirdest thing as a developer is the lack of full-powered editors running within Chrome itself. Cloud9 doesn't run on ARM yet, and Brackets isn't available as a packaged app. I'm personally fine using a terminal-based editor--I wrote most of Weir using Nano, and I'm getting more comfortable with vim--but it surprised me that none of the web-based editors have made a serious effort to run on a web-based platform.
The second-weirdest thing is the way Chrome OS distinguishes between "bookmarks" and "applications," considering that (for the most part) they're the same thing. There is a legitimate set of "packaged apps" that get more privileged API access, but most of the products in the Chrome "web store" are just links to web sites, so why can't I add bookmarks (such as the aforementioned XBox Music site, which I prefer to run in its own, chromeless window) to the Chrome OS launcher? I've been using this method to build single-serving Chrome Apps for the few sites where I want this ability, but it really ought to be built-in, and (considering that all you need is a JSON manifest and a .png file) I have a hard time understanding why it's not.
Oddities aside, though, the Chromebook is a great little machine for my needs so far. If I edited photos/audio/video on the go, or wanted a portable gaming laptop, I'd probably feel differently. On the other side of the power spectrum, if I didn't need a keyboard, I'm sure an Android tablet would cover a lot of my needs. My work, however, is almost entirely centered on text-editing in a web-friendly (preferably Linux or Windows) environment, and Chrome OS handles that gracefully and without complaint. It's surprisingly close to being useful even without Crouton. I'm excited to see whether (between Chrome OS and Firefox OS) the web platform can become legitimately self-sufficient in the future.