So here's my situation, I'm running ubuntu feisty (current) on a z61t thinkpad (945 card). When I have two displays connected (and X is using both of them). when i attempt to change the brighness via the keys or the /proc/acpi/ibm knobs the x11 segfaults.

I don't know if this ever happened before since I never tried it out.

Here's the important xorg.org excerpts: 

Section "Device"
	Identifier	"i945, head one"
	Driver		"i810"
	Option		"MonitorLayout" "CRT,LFP"
	Option		"DevicePresence" "true" 
	BusID		"PCI:0:2:0"
	Screen		0
EndSection

Section "Device"
	Identifier	"i945, head two"
	Driver		"i810"
	BusID		"PCI:0:2:0"
	Screen		1
EndSection

Section "Monitor"
	Identifier	"Thinpad LCD"
	Option		"DPMS"
EndSection

Section "Monitor"
	Identifier	"External Monitor"
	Option		"DPMS"
	HorizSync	30.0 - 81.0
	VertRefresh 56.0 - 75.0

	ModeLine	"1680x1050" 146.8  1680 1784 1960 2240  1050 1053 1059 1089
EndSection

Section "Screen"
	Identifier	"Builtin Screen"
	Device		"i945, head one"
	Monitor		"Thinpad LCD"
	DefaultDepth	24
	SubSection "Display"
		Depth		8
		Modes		"1440x900" "1280x1024" "1024x768" "800x600" "640x480"
	EndSubSection
	SubSection "Display"
		Depth		16
		Modes		"1440x900" "1280x1024" "1024x768" "800x600" "640x480"
	EndSubSection
	SubSection "Display"
		Depth		24
		Modes		"1440x900" "1280x1024" "1024x768" "800x600" "640x480"
	EndSubSection
EndSection

Section "Screen"
	Identifier      "External Screen"
	Device          "i945, head two"
	Monitor         "External Monitor"
	DefaultDepth    24
	SubSection "Display"
		Depth		8
		Modes		"1680x1050" "1280x1024" "1024x768" "800x600" "640x480"
	EndSubSection
	SubSection "Display"
		Depth		16
		Modes		"1680x1050" "1280x1024" "1024x768" "800x600" "640x480"
	EndSubSection
	SubSection "Display"
		Depth		24
		Modes		"1680x1050" "1280x1024" "1024x768" "800x600" "640x480"
	EndSubSection
EndSection

Section "ServerLayout"
	Identifier	"Default Layout"
	Screen		0 "Builtin Screen"
	Screen		1 "External Screen" RightOf "Builtin Screen"
	InputDevice	"Generic Keyboard"
	InputDevice	"Configured Mouse"
	InputDevice     "stylus"	"SendCoreEvents"
	InputDevice     "cursor"	"SendCoreEvents"
	InputDevice     "eraser"	"SendCoreEvents"
	InputDevice	"Synaptics Touchpad"
EndSection

Section "DRI"
	Mode	0666
EndSection