I have my hands on an XO laptop, the "One Laptop per Child" machine, a.k.a. The Children's Machine, a.k.a. the $100 (not) Laptop. Fellow tirekickers should review the project's wiki
I think the project is a sociological and policy disaster and a misuse of funds. (Can you imagine kids will really be able to keep these from being appropriated, stolen or sold?) I also think is a kind of Western intellectual-tech imperialism, if that word is not worthless from misuse. The proof is the interest Western techies have in it, and I count myself guilty.
I also think it's a lovely, rugged bit of hardware and wouldn't mind owning one myself. (But I'll probably get the comparable and now-celebrated Asus EEE in a few months.) And it is as tiny as advertized. 1411 grams and smaller than a study Bible.
Will go into more detail later. Don't have one? While it comes with limitations, you might try to emulate the Sugar OS on your own computer. Really kind of exciting.
Here's a real live image of me from a few minutes ago, taken from the XO's built-in camera. Full size. Gives you an idea of the size of the screen. FWIW.