I still use Terragen on my Surface Pro 2. Oshyan is correct, they are good for light Terragen work. I use it to test render for models that I designed with the Surface. Even modelling will stress the surface, rendering does it no favours at all. The device fan will become quite loud and the device itself fairly hot. They are really not built for that kind of heavy work, and unless it's plugged in, I wouldn't even use it for the testing I use it for, unless you want to watch your battery level drain in real time..
The Surface Pro is really a wonderful device, however. It is now being target-marketed (finally) towards the artistic crowd, as an alternative to the Cintiq Companion. It will do drawing programs in a pinch with the pressure-sensitive stylus. Modelling programs are also heavily supported as are image manipulation applications. Not to mention all the other windows-based programs in the world.