Just have a look at these 2 video's they show that virtual instruments on the ipad have grown close to whats on Windows.. same quallity, but a heap cheeper.
http://keyszone.boards.net/thread/400/icathedral-classical-music-ipadThe churchorgan is incredible versatile, and miroslav uses the same libraries as on PC..
Keep in mind tough, that when using the ipad as an instrument, you want atleast the 256GB version of the pro..