best, paint app for the tablet would be mypaint.
mtpaint is great, but the source is written in such a way that hildonizing it is a challenge that i failed at many of times.
mypaint might be easier to get hildon.
and it offers a gread deal of brushes...
and pressure sensitivity seems to work.

http://ee-staff.ethz.ch/~mrenold/mypaint/
for those who want to compile and take a look at it.