1) Try to make it sleep. (and wake up correctly)
2) Try to make it hibernate. (and wake up correctly)
3) Try to rotate a second screen into portrait mode while maintaining vsync and compositing. (choose any GPU for this, they all fail)
When you can do those 3 things reliably without fumbling around, breaking between upgrades, or even just do them (3 especially), I'll happily switch back to linux as a primary OS and say that it just works.
Still, Linux all the way since everything else is awesome!
Anecdotal illustration : I'm writing this from a machine running Xubuntu because of a relatively obscure Unity bug wherein the X server fails sporadically while, say, loading a text file. This most likely is a compatibility issue relating to my graphics card.
TLDR; I'm a fan, but it doesn't "just work".
In my ideal world, they'd maintain a custom set of drivers that could be updated on Arch, Gentoo, or a Debian variant.
I'd buy it, keep it updated, and never have to tweak. Like my desktops.