Thats why I stay with Intel graphics, they may not be the fastest graphics card in the world
but their Linux drivers never made any problems. Be it mode switching or dual-head, everything *just works*.
And that by using existing Xorg standards (XRandR, etc.), e.g. no nightmare "nvidia-settings" program as in the case for "the other" manufacturer.
And yes, for most models the drivers are open source, IIRC.