Reverent.org has an
interesting quiz that challenges you to tell the difference between music played by a computer and music played by a human virtuoso. Most people will probably find it pretty easy. I, however, scored only 63%. I mistook Rachmaninov for a computer (among other errors).
Comments
The problem with this test is that it doesn't do justice to what "MIDI" can do. The electronic examples are all quantized at 100% (meaning there is no room for tempo nuances) and played back through really poor quality general MIDI sound modules.
MIDI technology is FAR more advanced than this. Imagine, for example, the excepts played back on a Yamaha DiskClavier (which looks and sounds just like a "regular" piano, except it can be controlled by a computer) and with tempo fluctuations added using sophisticated computational algorhythms.
Furthermore, you can blur the distinctions even more by creating a "hybrid" performance- have a human "play" the score into a computer and have the computer edit the performance to fix wrong notes and to alter the tempo to increase the performer's "virtuosity".
(And if you're wondering, yes, major recording artists DO do the above all the time- a professional on ProTools can fool the ear just as well as an expert Photoshopper can fool the eyes.)