Such a zen experience. I bet this would be unbelievable satisfying if I owned a tablet PC!
I really liked the guitar "stings" during transitions between days. The music in general fits the game well - my only complaint is that sometimes the transitional bits clash with the ongoing background music. A little bit of fade-in/fade-out might go a long way. And that's a very minor complaint! I like the music, and the gentle buzz of the tattoo is kinda relaxing.
I had a few cases where button clicks didn't seem to register, (usually on the level-end receipt,) but otherwise this is INCREDIBLY polished. The second hand wiping away ink blots when I release the mouse button is a great touch.