I think this is a pretty good piece of software. It would be even better if you could make it function like a karyoke machine with the proper pitch of each note outlined on the graph. When you sing along, you would try to get the green line as close as possible to the outline. I saw an ad for some Windows software that does this, which is what made me download this in the first place.

The next thing that you could try would be to have the software automatically increase or decrease the frequency of the voice it is analyzing to force it to be on key. Then anybody could sing!