No Linux support for Nvidia Optimus is the only reason that I haven't bought one of the new T420s, and am still using my old Macbook.
I have been waiting for AMD Llano based laptops as I will be able to run them without any worries about switchable graphics. I need OpenCL and OpenGL support for work purposes.
btw, I use the proprietary nvidia drivers (just run their install scripts and it should work fine).