From the Web 2.0 Conference:
In the Chair is a music education service that enables students to play along with professional instructors and groups. Unlike linear CDs that simply have missing tracks (like Music Minus One), In the Chair's technology listens to the student and helps correct them when timing and pitch are off. (And it offers positive reinforcement them when they nail it.)
New at Web 2.0: In the Chair offers improved feedback technology and the capability for more instructors and composers to put their work into the program, in part thanks to a relationship with with the composing software company Sibelius. See www.inthechair.com/beta. The invitation code is "web20beta."
The professional musicians I know scoff at this idea, saying music beyond the most basic amateur level is far too subjective to be taught by robots. However, I remember learning a lot of basic piano with the Miracle Piano teaching system and really enjoying it.