Curiosity: For all those ethusing about this, do you have keyboard skills? Piano was my primary instrument and my take on this may be skewed by the fact my primary instrument also turned out to be pretty good for composing music with, when you can literally bash out full chords in real time if the mood strikes you. If your instruments were all single-note instruments that don't hook up to computers worth a darn I could see this being much more exciting.
When you write music with an instrument, often your ideas take on the idioms of that instrument, and the music you write is limited by your technique at the instrument. That's why I encourage composers to try writing without being at the instrument, as it gives you more freedom once you get used to it. This app appears to offer a compelling entry into that kind of workflow.
Composition by writing out rhythms and chords, and writing out multiple parts for multiple instruments, is just a different experience than playing it out on a keyboard. It lets you put more thought into how things line up and are organized, versus how they sound. That sounds downright unmusical but it's a big difference, I think.
This is just from my limited experience as a hobby composer sitting in front of a keyboard with pencil and staff paper, but I've heard it from other composers I know as well.
I did it with synthesizer and computer. What you say is still true, though, since that probably qualifies as yet a third way of composing.
For that matter I instantly noticed a difference going from ScreamTracker to a MIDI synth, too. Didn't even have an acclimation period, it was immediately of a different nature.
Some composers (especially those with perfect pitch) can write out music without an instrument. Mozart, Bach, etc.
Many composers that use a piano will also write out the notation by hand without a MIDI interface. In the scene[1] from Amadeus, replace Salieri's quill and paper with a stylus and the iPad/Surface.
I can see Staffpad software being useful for both types of composers.
Yes, I do but I'm stubborn in my current production process within Ableton Live Suite, but I have my reasons. As in I record single takes as audio files, not record MIDI inputs that would drive a synth engine. Well, I do that for drums but I finger drum naturally then build the drum line from clips/loops of my own usually with minimal corrections or quantizing.
Honestly I'd love to use this thing for Guitar Tab when sitting down and figuring out songs / covers. I still use pen and paper for that. Again, Ableton Live Suite has powerful tools to help - converting music to MIDI, both rhythms or melodies - but I do my own thing.