This new digital hand drawn animation software looks cool and promising... It's called Animation Paper. If you sign up for their newsletter before the end of March you will be offered an early bird price when the software is finished! There's no pressure to buy but at least the discount will be yours if you want it. Here is a link to an article about the software on Cartoon Brew.
I hope the onion skinning feature is decent... That aspect of digital software is often very frustrating. The creator, Niels Krogh Mortensen wishes to create "the world's most responsive, intuitive and powerful software for doing one thing, and one thing only: hand drawn animation." That sounds awesome. It will be available for Windows, Mac OS X and iPad. A responsive program with great pen sensitivity and brushes would be fantastic to have.
Man, I miss drawing.
Video of Animation Paper in use: