The aesthetics and convenience of wireless devices add to their appeal, but buying batteries (no matter how special) is a bummer. MacRumors forum user MarkBog felt so strongly about buying all of those batteries that he hacked his Magic Trackpad to use a USB connection.
To accomplish this feat, he removed the pad's batteries, stripped a USB cable down to the red and black power wires and then attached them to a battery-sized wooden dowel. He then pushed the dowel inside the pad's battery compartment and presto! It worked.
It certainly won't win praises from Apple, but it will save the hacker (and the environment) from a pile of batteries. Well done.