I think this is a great approach. It's interesting to note that they're pushing the same thing with Pugs, and it seems to be working very nicely. The catch phrase bantered around is usually something along the lines of, "I'll trade you a bug fix for a test."

Not only does it give a way to verify the bug fix, but it forces a bit more effort on the part of the reporter. It's not enough effort to be prohibitive (in my experience, anyway), yet it's just enough to raise the quality of the bug reports. All around, it seems like a really nice idea.