I found this comment on Dan Frommer’s post, The Real iPad, fascinating:
Same with music and audio gear. An iPad can become a set of audio mixer controls with a $10 app. With a $329 iPad, it is still cheaper than a hardware mixer controller, which is about $500. iPad can also be a piano keyboard or guitar for a few more dollars of apps, and the music data (MIDI) is sent over Wi-Fi to a Mac. I do my lyrics in Pages on iPad, sitting on a music stand. I used to carry a portable multitrack recorder, but now I carry iPhone 4S with Apogee MiC and GarageBand — it is cheaper, better, more storage, more battery, better microphone and analog-to-digital converter, more tracks, plus it has a full suite of MIDI instruments. So what has happened over time in my studio is that 2 Macs plus dozens of specialized music and audio devices have changed into 1 Mac and many iOS devices, and many audio/music-focused iOS accessories.