I'm in the process of building one of these. I may try to commercialize it on a small or large scale.
Its completely wireless and much, much cheaper than any of the available products I've seen like it.
Because I'm a nerd, I want to run a data mining algorithms on bar speed for various programming strategies and rep ranges and see if anything interesting pops out. With my product you just strap a watch like device to the bar, instead of hooking up a bunch of wires and annoying shit like that.
Another product out there is dartfish, that does all this by analyzing frame by frame video.