I can see why a wireless HD might be a good idea for the "coolness factor", but other than that I can't see how it would be of any great practical use. I mean, you're only ever going to access the HD when you're at a computer so, since you're already sitting in front of it, you may as well plug the HD into the computer using one of those HD caddies. There's never going to be a time when you need the HD to be wireless is there, because you're never going to be more than a foot away from a computer when you want to use it.
You might use wireless mice and keyboards as an argument against those points, but these devices are of use when made wireless because it means you don't have to keep tugging at leads when you're using them, so they DO solve a nuissance problem. A HD sits somewhere out of the way when in use, so there's no nuissance factor other than the hassle of having to plug it into a USB port to solve. Also, making a wireless interface for a keyboard or mouse is a cheap, simple process. Making a wireless interface for a HD is far more complex and in the real world would cost a hell of a lot more for no real end benefit. Another point to consider is that a wireless HD would need to plug into a mains outlet in order to be capable of transmitting so much data at such a high speed - battery power wouldn't really be a viable solution there. So even if you created a wireless communicating HD, it'd still need to plug in somewhere.
It'd be a good project from a challenge point of view though
Brian