I tried Unity on a netbook. The UI was fast, but unfortunately buggy. So, I end up using Kubuntu 10.10.
ATI still seems to have a problem keeping drivers easy to install and use. It has been this way for half a decade now. I installed them using the repository, using ATI binary, but none of them worked. In the end I left the repository one even though it did not enable OpenGL. I'll fight with it another day.
Nvidia on the other hand worked right away. I have a netbook with ION graphics, and the propietary Nvidia driver install without much drama. I just followed the instruction and voila. The rest of the time I use to watch CUDA demos.
So why buy ATI you ask. Well, not many times in my live have I seen a NO OS netbook being on the market. Asus 1215T on newegg (plug not intended).
Alas, freedom from the MS tax !