A friend of mine sent this to me. It is literally a virtual orchestra. Each orchestra member has a laptop instead of an instrument. Each "instrumentalist" designs their own "instrument" using a computer program, and the conductor merely provides visual cues for the "musicians". The group is SLORK, Stanford's laptop orchestra.
Having taken a bit of computer music myself, there is quite a variety of sound manipulation that is possible live, during a performance.
It would be interesting to see such a group.