The laws of physics won't allow you to use the Surface on your lap
The surface appears to be a very interesting tablet, but the common expectations of it to replace laptops are a bit off as from what I imagine, you cannot use the Surface with the keyboard on your lap!
It all comes down to physics. Unlike any laptop, the keyboard in the Surface is not rigidly attached to the display - it's a pivoting, elastic connection. Resting your palms on the Touch/Type Cover anchors down just the lightweight keyboard, not the tablet itself, and the tablet is standing nearly vertically up, on the edge of your knees, with a very high center of gravity. To make things worse, when typing, any shaky horizontal movements will be transferred from the keyboard to the tablet by the elastic connection and try to tip it over. And since the only contact between your lap and the device is on two edges perpendicular to your legs (the bottom and the kickstand), this will result in an experience so wobbly, that the Surface will probably be unfeasible to use in this manner.
It may be a very good tablet, but it's most applauded feature - the touch cover - only makes it the worlds smallest desktop, not a laptop at all. Of course, we are going to have to wait until someone tests this theory out, but until then I advice all on-the-go-typeists to keep their hopes from flying too high.