Xenon Labs (http://www.xeapps.com) has just released Symphony Pro for the iPad, which is the first “real” music notation application I’ve seen. The best part is that it saves files as midi files or as music XML files, and both can be opened by Sibelius. I’ve not had much time to experiment with it yet, but it has better features than anything else out there.
Is it as efficient to work with as Finale or Sibelius? No, but neither is this typing on the on- screen keyboard compared with a physical keyboard. However, as with many other uses for the iPad, it’s not that it does it better than a computer app, it’s that you can do it in situations where you can’t use a regular computer as easily or as comfortably.
One other note: if you, like me, used to watch “Star Trek: The Next Generation,” and you watched Commander Data’s android fingers fly over those glass control panels at blinding speed, you probably love typing on this virtual keyboard anyway!