Surface: Core or WPF
The Surface SDK comes with two API’s: WPF and Core. The core layer appear to be suitable for any UI framework that is HWND based (e.g. XNA) and appear to be the correct API if your Surface application requires high-end graphics e.g complete 3D animation. Reading the SDK documentation, the WPF layer appears to be the layer of choice; offering numerous custom controls, and the advantage of using Blend 2. The Surface SDK offers WPF touch-enabled versions of Window, Button, ListBox, TextBox etc
Surface Simulator does appear to take a good chunk of CPU – well it does on my Dell. It’s also nice to see Microsoft ship appropriate functionality to automate testing of Surface applications. Microsoft has also done a good job of providing 15 samples, together with the standard “Hello World” 
Hello
Is a Surface SDK available for download somewhere? I can’t find it. Or is it available only after you purchase Surface table?
Thanks, Tom
Unfortunately I believe you have to buy the Surface to get the SDK
You will be much happier prototyping the UI in flash/after effects and then hard coding in XNA/C#.
.wpf if pretty clunky when you are working with a lot of content on Surface.