Well, these panniers aren't quite entirely made of duct tape, but they sure use a lot! Kent Peterson put up a great page detailing how to make these duct tape panniers. The concept is pretty simple and definitely hackable--there ought to be tons of variations on this same design.
The basic idea is to acquire a couple of plastic containers--Kent used pet food containers. Cut the top at an angle, so that when the panniers are mounted the bottom of the pannier is farther from your heel. Find an old political campaign sign, or Realtor sign (the material is called coroplast) and cut a couple of tops for your new panniers. Kent used zip ties to attach the lids to the bodies. In order to hang the panniers from his rear rack, Kent used some double shower hooks (refer to his pictures for a better visual explanation) mounted to the pannier.
Seems to me that this would be the weakest part of the design since pretty much all the weight from each pannier is hanging on those shower hooks. Kent's pictures don't show it, but the hooks seem to just be screwed in through the plastic with little reinforcement. Should be fine for relatively light loads, but I'd imagine a few books in the pannier could start to cause the pannier to hang low and possibly slip off the rack.
Kent keeps the whole business strapped down with bungee cords and spare toe clip straps. The toe clip straps are mounted near the hooks in order to keep them tied down. The bungees wrap from the rack, around the pannier, and back onto the bottom part of the rack braces.On the whole, it's a really cool idea and a relatively inexpensive set of panniers. Kent mentioned that he'd been considering Oyster Buckets (or, for Portland folks, some BikeBuckets), but his design definitely offers more heel clearance, which is a must for a bigfoot like me.