A nice little read in this Computerworld article. One OLPC on it's own is a nice machine but two or more together and you can immediately see some really spectacular stuff.
When the OLPC idea was first announced one of the richest men in the world contended that the same capability could be had via mobile phones... which missed the point entirely as the areas that these things were designed for had no, and are unlikely to get, any meaningful telco infrastructure. The mesh networks the OLPC runs make all of that redundant. Power them up and you have a network infrastructure... put a repeater in a tree and you have a village wide network... put a repeater in a tree every two km's and you can talk to the next village.
Of course there are other ways to do the same thing and some may even be as cheap, but it's still a very, very impressive thing to see in action.