I had the XO for a few days now and I had the opportunity to play with it a little bit. The device is small; smaller than I expected. And, yet, it packs a lot of punch for the size and the components inside. It's definitely slower than your top-of-the-line two core machine, but you are not left twiddling your thumbs while waiting for things to load.
The screen presents great sharpness of image and is big enough for 99% of the tasks that I will ever perform with it. I'm not going to use the XO for extensive programming tasks, for instance. But the XO is great to take on trips with the family just to check on email and surf the web.
I have large hands, so the keyboard is unusable for me. Thankfully, I can easily plug my HHKB into one of the three USB ports and use it instead.
It comes with a built-in wireless network card that connects right up to my wireless network at home. I also read a little about the mesh networking capabilities of the XO, but haven't had the chance to actually play with it first-hand yet. Mesh networking is a fascinating technology, though.
A little perk that comes attached to the XO version that I have is the free year of T-Mobile HotSpot access. I activated mine today and it works like a charm.
The OS is a modified version of Fedora Linux, so I'm sure it is highly customizable. This weekend and the next few days I will be doing a lot of reading at the Laptop wiki site. They have an amazing amount of really great information about the machine itself, as well as projects and lessons to do with the kids. I also found some very useful posts by Bill Clementson about his experiences with his XO.
Anyway, I will keep you posted.