I've had a little time to play around with the new RandR 1.2 support in ATI/AMD fglrx graphics drivers and I'm liking what I see. Make the laptop run with dual external monitors or the in-built panel is now really easy. It's a massive improvement over the ati-config approach I was using before.
Here are the commands I used to make the my Dell Studio 1535 run with dual external monitors:
xrandr --output LCD --off
xrandr --output CRT1 --right-of DFP_EXTTMDS --auto --output DFP_EXTTMDS --auto
These commands will now make it run with the laptop panel:
xrandr --output CRT1 --off
xrandr --output LCD --auto --output CRT1 --off --output DFP_EXTTMDS --off
Now I just need a nice way of attaching these commands to the screen setup button on the laptop :-)