it is unclear to me even after reading the nouveau wiki what support is provided for twinview, quadview, and xinerama?
e.g. i have a quadro nvs 440 (NV43). the proprietary driver (under fedora core) drives four physical displays. each pair of screens is combined into one via twinview and the pair of twinview displays are combined into one logical (four physical) displays via xinerama.
while this isn't optimal (e.g. no xrandr support because of the xinerama), it is workable.
can nouveau do anything similar yet?
My experience (with two displays on two gpus): xinerama works as expected if you disable compositing, otherwise it will be stuck in clone mode. No 3d acceleration, though. To have 3d acceleration you can use different x screens (zaphod mode). Don't know about xrandr (as it doesn't support multiple gpus yet).