can anyone fill me in on the Raspberry Pi?

I was browsing eBay for some clear plastic boxes and saw a case for something called the Raspberry Pi and got curious. I found out it's supposed to be a mini Linux PC that's little more than a circuit board, some input and output slots and an SD card slot that runs off the SD card, and they're rather cheap.

My question is... are they functional enough to be worth $40 or so? I'm aware a computer with very limited RAM and using SD for a hard drive probably isn't going to replace my current PC at all, and won't be a gaming machine much with low RAM and Linux(I've heard it can run Minecraft, although with low onboard RAM and probably a basic graphics chip I doubt it'll run it well given how poorly it runs on my PC) but if I wanted, say, a backup computer that could go online and such if my main PC were no longer usable, would it be worth the cost for it, or would that money better go to something like a Windows tablet? I'll admit I'm 100% unfamiliar with Linux so I don't know how it compares to Windows in function or feel.

I've watched some Youtube videos, checked the official site but I want to know from people who may have actually used them if they're worth buying. I don't like throwing money around blind even if it's just $40.

A recent issue of Maximum PC magazine's print version had a couple of detailed articles on setting up and using the Pi.

Just saw this article on the Pi. The site the article is on has had other articles about the Pi.

I got mine back in June- set it up with XBMC as I don't have satellite TV. I also keep a second SD card loaded with Raspbian in case I need the desktop OS. My total cost was about $100 for the board, case, couple of SD cards, power cord, HDMI cable, remote and IR sensor, etc.

There are more powerful boards out and coming out, such as the Cubieboard, but they lack the software dev community to make them worthwhile yet. That better CPU and GPU won't mean anything without the software to make it worth using. Give it maybe 2 years though and we might see a flood of worthwhile competitors.

I've been eating Pi since last fall. I have three of them now, about a $100us to set up with wifi, mouse, key board, sd card and psu. Amazing little machines. I use one for still motion camera work, one is a media center with XBMC, the third is just to play with and learn more about Linux. It has inspired me to install three Linux distro's on my lap top.

Linux gui's are not as polished as MS stuff, but they do look good, have tons of FREE software and run fast on PC's