I've been playing around with it for a couple months on my iPad. There was even a guy using his iPhone as a MIDI controller on TV last night. However it's a lot of reading and experimenting to make functional. Right now there's no ";keyboard"; layout, but you could build an interface with many small pads that trigger different pitches/sounds.
I have it set up with Logic. It works really well! Apple implemented a native use for it, so you just set it up as a control surface and it's capable of controlling most of the parameters you would need.
In terms of using it as a MIDI trigger pad, I have not tried that. I'm sure it would work fine... you'd just have to use OSCulator to translate the OSC messages into MIDI notes, and then use that input into Sib. or Finale.
It's a really cool program! Lots of potential there, for sure.
Jim and Crew- That's a thought too... There are some iOS programs with accompanying server programs that run on the computer. It'd be cool to have a VDL control surface app! Pretty much an interactive Keymap on your iPhone.