I use Lenovo Ideapad Z580A with hybrid video: GeForce+Intel with Ubuntu 12.10 x64 Ukrainian. It has internal display and two outputs: HDMI and VGA. When I connect third display to VGA all displays go black. Pressing alt+backspace and login causes output to two displays: internal and VGA. System Settings -> Displays (or monitors - I have Ukrainian interface) shows three displays: two are on, one (DVI) is off. Turning DVI on and pressing apply causes an error: Can not set configuration of controller CRTC 65. BIOS setting is Optimus (two video cards). Driver for GeForce is Nouveau. With best regards. Viktor.
on my workstation i have a similar configuration, core-i7 (internal graphics) and external gtx. All Three outputs (2xgtx, 1xintel) seem to only work since 3.8-kernel, which comes with Ubuntu 13.04. you should try the mainline-kernel from
looking for other seetings then optimus in BIOS could also be worth a try.