Wonderful interface, USB but worthless in some application.
Ever since ver 2.0 usb was introduced some misguided folk have tried applying it to applications not suited for such slow interfaces.
Chief among these are external hard drives. Apple is quick to caution the use of USB for external boot drives. They are too slow and will not work because they are so slow. Firewire is the answer.
One of the best deals out there with regard to external drive enclosures is the $25 VOX enclosure that does NAS, USB, and firewire. It works well in all modes but does not limit the user to the slow USB mode.
We have been using a VOX external drive enclosure with a medium sized IDE drive for about a year now running it over firewire. Works great. Just recently got the drive set up on NAS. That works great too and eliminates a box and cables around the ibook notebook.
Using airport wifi interface, we now have wireless access to internet as well as serious external storage.
Well worth the $25 it cost for the VOX unit.