Fred
You can NOT move or backup images from your iPad onto a regular HD trying to use a USB connection . There is no direct USB port on an iPad.
Hopefully you got the 64G version - you'll loose about 5G to the operating system and have the rest for storage
There is a nifty backup device made by HyperDrive.
http://www.hypershop.com/HyperDrive-...rive-s/183.htm
The HyperDrive iPad Hard Drive works thru the Camera Connection port on the iPad. My understanding is that you can read/store images from a CF card directly onto the Hyperdrive (up to 750GB), then can connect the HyperDrive to the iPad for viewing/export. But suspect you can only download images from the Hyperdrive to the iPad (ie - can't move images or files from the iPad to the HyperDrive).
I have a unit on order (case only) which should arrive next week. Plan to drop in a SSD or 500Gb HD for far less than what they're charging, and then see how well it works.
Given you have a Mk4, you also have another option. Use a 16GB SD card as primary storage media in Mk4, then use the Apple Camera Connection Kit (which has SD card reader) to import files onto iPad. Given how the cost of CF cards has come down, you can use the MK4 to copy the SD card onto a CF card in the camera, and then use the actual CF cards as your backup storage media. It all depends how many images you plan to shoot.
Either way, you shouldn't have to still cart along your laptop.
Hope you enjoy the iPad2