A word of warning for anyone buying/building a PC with a Core2 Duo-supporting motherboard: the Linux kernel in Ubuntu hasn't been patched yet to support the way these motherboards handle PATA (aka IDE) drives, so neither the Dapper release nor current Edgy builds (as of a couple of days ago, anyway) will install if the DVD/CD drive is PATA. With a SATA DVD/CD drive (and SATA hard drive, which is more common), Dapper installs and runs fine.
Update... updating to the newly-released Edgy Eft beta went fine, just had to make sure that the hard drive was connected to the JMicron controller (2 purple ports on this motherboard) rather than the ICH8 controller (4 yellow ports). The update fixed the timer problem I was having as well, where the system clock and Xine audio playback were running too fast.
Update (2006-10-10)... thanks to Ben Collins all the drive recognition bugs appear to be fixed: I can see SATA/JMicron, SATA/ICH8 and PATA/IDE drives again now.