This is based on Harmony by MrDoob. Example: http://mrdoob.com/projects/harmony/ Fork on Github: http://github.com/mrdoob/harmony Its a great bit of work, the brush engine is simple to pick up too. I really wish deviantART would fork the github repo, its not a drastic departure from the current source. i'd love to see how the WACOM integration works! I wonder how many people have paid for the extras in the DA version…
edit: My mistake. It detects when you're using the eraser, but that's it.
edi2: Actually some of the brushes do seem to be pressure sensitive but it doesn't seem to work on all of the brushes it should.