I have moved to Debian as my primary distro and using squeeze (currently labelled testing, but soon to be stable) on my laptop. Unfortunely my laptop has a nvidia graphics card, and it pains me to have to enable the non-free repositories. Virtual Richard Stallman (vrms) got pissed.
On laptops, there usually is a Fn button to change between displays. On nvidia hardware, there is an ACPI event sent that the nvidia driver reacts internally to. This does not happen in the current driver in squeeze and was a major flaw for me. Using acpi_listen i saw that there was no acpi event even sent out. (This worked fine in Ubuntu, acpi event and everything).
Then I found disper: http://willem.engen.nl/projects/disper/
It is meant to switch between video outputs and adjust the resolution automaticly.
To get the image on the laptop screen:
disper -s
And to get it on the LCD screen (connected with VGA in my case)
disper -S