They are really annoying on Linux.
For me, the palm rejection has never worked as well as it does on Macs and the scrolling and multi-touch gestures are so pathetic under Linux on a laptop that its better to just disable the touchpad and stick with a mouse.
Even the glassy smooth feel of the Mac touchpad is superior to other laptops and the new haptic touchpad on the newer macs makes clicking on any part of the touchpad wonderful.
I do have a question for HN: with enough practice, does a keyboard with the pointing stick ever feel adequate? I've never seemed to get the hang of it in the numerous times I've had to use them (each time for only a few minutes).