Check out this demo for Melodyne's DNA (Direct Note Access) technology (not yet released). There already are programs that can change the pitch of single notes in a mono audio recording. This is different. Their demo shows them changing single notes 'inside' a complex, polyphonic guitar passage. You can change the pitch of individual notes, move them backward/forwards in time, mute them, etc., just like you can with MIDI.
The implications of this seem stunning. Gary, am I right that this is a big deal? Or maybe I just need to get out more?