I've got about 8 or 10 (evenly between guitar and piano). I was stoked with the basic lessons, although my frickin' fingers now hurt. This is one of the best things Apple has done in a while. It's hard to learn how to play guitar without taking lessons, even with an extensive musical background.
All that needs to happen now is getting more artists aboard. A little Chris Cornell would rock, assuming he plays the guitar.
I play the piano and found the Piano not suitable as an instrument to learn as they teach it (chords)...
Which songs/artists do you have access to buy? I can only find one guitar song to buy. I hope the other (upcoming) guitar lessons will be more "advanced" .