If you have an iPad lying around, I recently made an app called Composer's Sketchpad that uses this sort of notation to its fullest. You "draw" notes directly onto a logarithmic pitch grid, and instead of having to snap to the usual array of discrete piano-key pitches (ABCDEFG), you can start your notes at any point on the y-axis and arbitrarily pitch-bend them as you draw. I've found this to be the perfect interface for playing around with musical ideas, and particularly useful for writing out expressive solos — something staff notation is just terrible for!

Homepage: http://composerssketchpad.com

Trailer: https://www.youtube.com/watch?v=ypsLgTY8NXs