Hyperdrive will back up to a usb hard drive with the adapter kit, however the drive must be configured as FAT. the commands are not exactly obvious and it took me a conversation with Hyperdrive to figure it out.
if you buy a Hyperdrive, buy only the case and buy the drive separately to save yourself $100 or so.
however, i always take a laptop and have never yet had to use the Hyperdrive other than as a usb backup drive to the computer (since i've spent the money on the Hyperdrive the computer won't fail). I feel very uncomfortable if i can't review images at least every couple days and preliminary sorting, editing, keywording, captions on the trip save me a lot of time when i get back. i also need a computer to add location from my GPS logger.
on a short trip a bunch of CF cards might be okay (as long as you don't loose some), but it there's any action, i can easily fill a 32gb card with 5D3 images in a day