Nit-pick: the "Ultrabook" brand specifically means an Intel CPU with built-in GPU. Even outside the brand, there aren't many laptops with that form factor with a non-Intel GPU these days.
Having said that, for window compositing the open-source radeon drivers seem to work fine as long as you don't go for a bleeding-edge chip.[1] For games, the proprietary nvidia drivers are likely better and might be worth the extra hassle (but realistically, booting into Windows is less hassle and gives a bigger choice of games... Also, realistically, you won't get a powerful 3D chip in a thin & light laptop).
[1] I've never tried the open-source nouveau drivers for nvidia chips; they have apparently been improving in leaps and bounds.
"Ultrabook" currently specifically refers to a system with a Sandy Bridge or Ivy Bridge based ULV CPU, all of which have integrated on-die GPUs.
Re the announced system: interesting - does Optimus work on Linux these days then? Last time I checked, the GPU on Optimus systems was dormant on Linux.
Having said that, for window compositing the open-source radeon drivers seem to work fine as long as you don't go for a bleeding-edge chip.[1] For games, the proprietary nvidia drivers are likely better and might be worth the extra hassle (but realistically, booting into Windows is less hassle and gives a bigger choice of games... Also, realistically, you won't get a powerful 3D chip in a thin & light laptop).
[1] I've never tried the open-source nouveau drivers for nvidia chips; they have apparently been improving in leaps and bounds.