If Auto-Tune can operate live, it opens up a lot of possibilities, like singing a duet with a good version of yourself, or singing in harmony with yourself. Or singing with versions of yourself as Barry White and The Chipmunks. You could also end up with a live concert that is basically someone on Singstar, and you could easily gather statistics about the performance and display them to the singer like "You're 2.3% off-key today, by average". If you were feeling very geeky and self-degrading, you could display those same statistics to the audience as "90% of what you're hearing right now is real".
Mokalus of Borg
PS - I doubt many performers would opt for that last one.
PPS - Unless they were being deliberately ironic.