I think collbative recording can work well. My iPhone app, Jampipe, is kind of a scratch pad for musicians. Quality isn't the top priority, the main focus is on collaboration. Not sure about drums but most instruments pick up well with the iPhone mic. I sent you an email by the way!
I don't think these digital textbooks will take off on a closed platform. The iBooks format is based on ePub so I think there's every chance you'll see these books reaching other devices over time.