I have one of the laptops that Google originally distributed in order to test Chrome OS. As the idea behind a Chromebook/box is new to some, I thought I'd focus on the operating system, though I've covered the hardware to a point.
I'll try to make this in-depth without it being too technical.
If you're looking for a quick idea of whether or not this is for you, jump to the bottom and read the summary.
The premise on which Chrome OS is based is that almost everything you do when you use your computer happens in your browser, so Google have built a system that makes that experience as fast, as simple and as secure as they can. That simplicity also leads to an 8-hour battery life, which very few laptops can offer.
This simpler approach means that you don't have to deal with software updates(with one exception, see below) or worry about anti-virus software.
This also means all of your files and media is stored on other computers, on the internet. Some people aren't ready for that and if you're not, a Chromebook/box isn't for you.
Applications and Limitations
As you might imagine, just the web means no Windows, Mac or other typical software applications. Because of this, there's no CD or DVD drive in a Chromebook/box.
Though `just the web' may sound extremely-limiting, you can do a lot in your browser; multimedia editing(including video), as well as voice and video chat is all entirely possible on a Chrome device, as is the creation and editing of documents, spreadsheets and presentations. This software is available all over the web and there's a selection of useful tools to be found in the Chrome Web Store, with free and paid solutions.
That said, you can just type in a web address or search as you would normally to find a helpful website. As an example, Google, Zoho and Microsoft all offer web-based office suites, some of those are free and some paid.
Setting up a Chromebook/box is as simple as turning it on, putting in your Wi-Fi(or plugging in an Ethernet cable) connection details and logging in.
If there's a new version of the operating system(as there was when I set my machine up) it will download that before you can continue. This may seem odd, as the idea is to make updates invisible to you, but a Chromebook/boxes check for updates the first time they're run in case something in that update changes something key, like the introduction process for new users.
Once the laptop has checked for updates, it reboots and you login. You're then shown how to do various things with the click-able touchpad, such as scrolling and right-clicking.
After the first time it's turned on a Chrome device is designed to be very fast. In my experience, that means booting up in around 9 seconds from off, whether that means the power button being pressed or the lid being lifted. If you close the lid for a while but leave the machine on, it should resume instantly.
Whilst not being able to install traditional software can seem restrictive, it also has a huge benefit: no more anti-virus software.
Viruses are so common on Windows(and lately the Mac operating system, OS X) because the more software that's installed, the more potential vulnerabilities there are to exploit.
Because the a Chromebook/box knows what software should be installed, it can keep a copy in an encrypted area of the hard drive. Each time you turn the machine on, it checks to see if anything unathorised has changed in the software. If it has, that encrypted copy overwrites everything and any updates will be installed when you connect to the internet.
No system is 100% secure, but this method(called verified boot) makes it much harder to compromise your machine.
Privacy and Google
Some users don't like the idea of being dependent on any large company for their computing needs. So, does a a Chromebook/box make you reliant upon Google?
In short, no. Whilst Google does encourage you to log in to a a Chromebook/box with your Google account, you can log in under Guest mode. Whilst using Guest mode, nothing you do is saved on the machine, you don't need to log in to a Google service and you're free to use any web-based service you choose. Google is currently working on other login methods.
However, should you choose to login using your Google account(as I do and most users ultimately will) your settings and bookmarks can be saved and synched across any other device running Chrome(which now includes Android phones running Ice Cream Sandwich - version 4.0 of Android - and above), just as they are in for the Chrome browser.
Files and Devices
A key thing when using a system like this is being able to use files people email you and external hardware, just like you would on a Windows PC or a Mac.
If someone emails you a picture, for instance, you can download that file and directly upload it to Picasa Web Albums, Google's photo hosting site. This is called a file handler(think of it like you would a piece of software that opens certain files in Windows) and Google has released tools for companies to do similar things with different file types. For example, Google Docs will soon be able to upload Word documents, Excel spreadsheets and Powerpoint presentations directly to your account, without needing to go to the web address of the service.
I've tried various hardware with my test laptop. All have worked well.
Inserting a usb thumb drive or plugging in an external hard drive will make a a Chromebook/box scan it for files it can play(there's a built-in media player) and plugging in a camera will show you the pictures on it. I've also tried an external webcam, microphone, keyboard and mouse and my Android phone. All worked as I expected.
Chrome OS is great when you have internet access, but what about when you don't have internet access? Many(but by no means all, yet) web sites can work off-line and then upload your game progress or document when you next connect. Some of the applications that currently function off-line include the NY Times, Google Docs/Drive, Huffington Post and Angry Birds.
Hardware and Pricing
Those who dislike a Chrome device soften bring up netbooks. A netbook is a small, cheap laptop which almost always has low-quality, slow hardware. This results in a poor experience, as they typically run Windows and because of their cheap hardware, can't provide the resources Windows needs to run at its best. On top of that, Windows can't offer the security that a Chrome device does, can't boot as quickly and very rarely will you find any laptop that run for 8 hours on a single charge.
Right now, Google has only 2 partners who are making Chrome devices. That lack of competition keeps prices higher than they likely will ultimately reach.
My experience with the test machine Google distributed(called the Cr-48) from a hardware perspective has been very positive; my Windows 7 machine(running very little software) boots in just over a minute. My Cr-48 is at the login screen in just under 10 seconds. Depending upon the task, I've experienced between 8 and 10 hours of use per charge.
It's similar to the machines you can buy in that it has the same quantity of memory and storage and a similar sized(though not as hi-quality, I'd imagine) screen. The major difference is that the Cr-48 has a single-core processor, whereas the official Chromebooks use a dual-core chip, making them better able to handle more intensive tasks, such as video playback. There are newer devices now available that offer more RAM and quad-core processors, making them even faster.
To put it simply, Chrome devices are fantastic if you use only the web or spend almost all of your time on the web; sub-10 second boot, great security and great battery life.
If you don't or don't have internet access most of the time, these aren't for you just yet.
As of August 2012, Chrome devices have a vastly improved interface, incorporate Google Drive as part of the file system and allow the creation and editing of Google Docs without an internet connection. The software is slowly improving(every 6 weeks) and more and more applications are becoming available without an internet connection. Unlike your Windows PC or Mac, a Chrome device you buy will get better over time and won't charge you for updates to the software.