APC has a nice little tidbit with more info on the new Macbooks, including this wonderful nugget:
The new MacBook (and Pro) are the first notebooks from Apple to use a SATA optical drive. This means that if you were prepared to jerry-rig it up, you could actually take out the optical drive and put a second hard drive in there. Yes, that means you could potentially have a MacBook Pro with 2 x 500GB hard drives – 1TB of storage in a slim, non-chunky laptop. The pic on the right is from the excellent MacBook Pro disassembly by iFixit.