I recently upgraded my MacBook Pro to Kubuntu 8.10 beta with the shiny new KDE 4.1. Along with this update came xorg 7.4 which does not rely on xorg.conf for device configuration anymore. From what I can tell, this is abstracted by HAL in order for the devices to be hot-(un)-pluggable.
Anyhow, I used to have many synaptics settings in xorg.conf that enabled two finger scrolling, two/three finger tapping with my touchpad. But because these settings don't go into xorg.conf anymore, here's how you can fix it (took me a couple of hours to figure out):