This article in The Economist is very interesting.
We've been watching this issue closely. So far, the alternatives to OLPC's XO computer measure up on price or features. But that may very well change sooner, and probably will change later.
That's fine. The Waveplace courseware we're using in Immokalee and the Caribbean can be used with any computer, be it XO, Mac, or PC. So the device we use does not matter one bit.