It looks like it wasn’t quite the perfect time I thought to order a PowerBook. I received confirmation today from TerraSoft that the delay is due to the changes in the PowerBook line (which were half the reason I chose now to order it). It seems they’re still waiting for a shipment from Apple!
Presumably they had some in stock when they updated their store, in which case this is probably a good thing: it means not only are the new PowerBooks selling faster than expected, but they’re selling well through a Linux shop!
That said, if I have to wait too long I may just cancel this order and drive down to the Apple store. Of course, then I’d have to deal with repartitioning and trying to set up dual booting myself, and not only is it more complicated than dual-booting a PC*, there’s a lot less information available.
* In particular, I don’t know of any utilities like Partition Magic or Parted that will allow you to resize an active Mac OS filesystem, so I would have to wipe the disk and reinstall Mac OS along with installing Linux.