It's a Toshiba AC 100 with an ARM-based Nvidia Tegra processor and Android operating system in a standard netbook form factor. I don't believe it's available in the US though, if that's where you are.
First impressions: it's very light, to the point of wobbling around when I type with it on my lap. Many of the peripheral keys are very small for my Western fingers, although I feel I'm getting used to them already. It's fanless, and has only flash storage, so it's eerily silent and apparently gets up to 8 hours of battery life. The trackpad doesn't have enough vertical space to be comfortable, and there are neither function keys nor a delete key, although there are a whole row of special keys which presumably can be xmodmappped.
The online reviews mention that Android provides a less than elegant interface with the lack of a touchscreen, and I agree; I was planning to install a Linux or BSD OS on it all along. As I understand it, that's pretty tricky; should make for a nice weekend project :-)
As for why there aren't more of them around already, my best guess is that OEMs don't want to piss off Wintel by selling what is effectively a PC which doesn't use their platform, for fear of losing the discounts and rebates they get when they do. I hope I'm just cynical and there's a better reason; for casual use the system resources definitely seem adequate. Acutally, as soon as I get a proper OS and WM installed on this thing, I can easily see it taking up half of my computer time, and it will be brilliant for having a quick hack on the go...
[edit]
After the first half hour or so of usage, it's clear that the Android as currently installed is definitely not a good fit for a non-touchscreen, full-keyboard device: After 5 seconds of idleness, the screen dims, then blacks out completely, just like a phone would; navigating through screenfulls of icons using keyboard or mouse becomes tedious very quickly, and to top it off I've run into a few bugs as well.. This thing is begging for a linux/bsd makeover, hopefully I will uncover a real beauty...
That said, the rumor is that Chrome OS is only going to ship on ARM, and will do so Real Soon Now. I'm not convinced that Chrome OS is going to be a hit, but I can see more people being willing to give up Windows for it than for a typical netbook Linux distro.
Also, the processor is not responsible for a huge part of the power consumed on a netbook. Disk, screen and memory seem to be a big part. If you make a netbook that can run Gnome and Firefox decently, it will have a hard-drive (or SSD) and a couple gigabytes of memory. The LCD is the same.
So anyone like Asus or Acer that have a PC business and launch a non-windows netbook soon learn the error of their ways.
Of course, Microsoft will probably find a way to increase their OEM pricing, specially if the Windows-proof line ends up making a dent on the Windows-bundled lines. And they don't even need to increase, say, Asus's licensing prices. All they have to do is to lower Acer's.
The Windows-based netbook market?
When I only do word processing or browsing simple web pages, I never have to read data (everything is cached). Laptop-mode also delays writing data back.