Last weekend Jill wrote a quick little post complaining about a music tracking service. It has been years since I've rehearsed a musical (turns out that karaoke host was right, and people really don't want to hear me sing) but even I know that the piano accompaniment of my youth has disappeared into a vast array of tracks and music software services. So enlighten me! What music services do you use for rehearsal or performance? Which ones do you like best? Why?