If you have a mac, buy this. ^^^
I have two 500 gig WD drives that I've maxed out (they have USB 2.0 connection ports). I learned from experience that firewire is definitely a lot faster than USB.
When you import your videos, import them straight to the external hard drive. Then, when you go to edit, leave all of the files on the external drive and save the video project to the drive. Video files on your Internal hard drive will eat it up in no time.
This drive is worth the money in the long run.