As a big fan of the ipad in general i have come to the conclusion, that the ipad is unfit for making computer based music, because it can only run a single program at once, background programs are halted..
Its nothing but a toy.... And the keybed does not change anything about that.
If you want to have a tablet for real music making, have a look at the microsoft surface pro 2.
Ipad is a perfect musicreader, and a nice toy to play with ( including music toying ). Its just not fit for professional music making, it does not have the freedom of a PC and lacks the interface of a professional instrument.