Yo!
Environment: Matrox G550 on xorg from unstable on a (mostly) sarge
installation. 2 analog screens. Xinerama is used, bare xorg - no mga_hal
etc.; kernel linux-image-2.6.12 or kernel-image-2.6.8 doesn't matter;
686-smp in both cases. DRM loads fine.
Symptom: booting, one display is text console. When X is started, it
starts fine on that display, but there's no signal on the other display -
thus it won't even come out of power save mode.
Starting X once with a single head xorg.conf solves the problem: The 'single
head' X delivers identical signal to both outputs of the graphics card
(even to the point where killing X or switcing back to text mode shows the
text mode on both screens). Changing xorg.conf back to the
dualhead/xinerama one, it starts fine on both displays.
[ please cc: me on replies ]