I described my early experience with the HP Touchsmart tm2 - 2000ed in my earlier post. Here's some updated info: since my last post, a lot of Linux developers have made the experience even more pleasant.
Ubuntu Maverick has some issues because the two graphics devices interfere with each other. It turns out to be very easy to turn the Radeon driver off at startup:
echo blacklist radeon | sudo tee /etc/modprobe.d/blacklist-radeon.conf sudo update-initramfs -u
Alternatively, you could install all packages from the Radeon xorg-edgers ppa. Their new xserver-xorg-video-ati version does not seem to have these problems. You will also notice that it works a lot faster with 3d applications (I tested with flightgear). It says on the lauchpad page that you need a 2.6.36 kernel for this to work, but for me it is running fine on stock Maverick 2.6.35. Caution: this driver is still under heavy development. For example, my external monitor does not work and there's problems with material shaders in flightgear.
There's still a bug that sometimes the backlight does not come on when you start your computer. Here's the bugreport. In the comments to my last post, Mike noted that you can just close and open the lid, and the backlight comes back on.
Install the synaptics-dkms (version 1.1.1) package from this bugreport. The clickpad button will still not work, but at least you have second and third mousebuttons with two and three finger taps.