I have an office issued thinkpad W500 laptop which has "switchable graphics"
That is, on OSen that support it, such as Vista / Win 7, the graphics processor
will automatically switch from an ATI Radeon to an onboard Intel 915 when on
battery / in power saving mode etc. There are two graphics processors installed
that you can switch between on the fly.
On the ubuntu lucid that I just installed on this laptop, it detected and used
the intel agp card, providing rather slow, jerky video. When I tried to use
radeon for my X - either using the open source ati / radeon or the closed
source fglrx drivers, X locked up solid .. black screen.
And thanks to ubuntu being super helpful about launching FAST into an X session
(gdm) without showing you things like grub boot menus, etc .. well, that meant
I couldnt even get into the laptop (I could ssh in, remove xorg.conf and
restart gdm, after which it got back to using the intel card).
After breaking my head over Xorg.0.log multiple times, I at least came to a
very interesting entry that said "disable switchable graphics in the bios". I
did that - and it immediately booted into X using the ATI card.
A little digging I did after that came up with these useful links which I plan
to try out later rather than sooner (it being my work laptop, a little caution