Got it working.

I didn't know that there were special other instruction in the first post to get this app working. I just assumed if I download something from the app manager, then it should just *work*?

Anyway, did the following:
as root:
apt-get install libblas3gf liblapack3gf pymaemo-optify python-numpy

Are blas and lapack fixed in extras-devel?
(Fix broken blas and lapack for python-numpy:
as root:
cd /usr/lib/
ln -s libblas.so.3gf libblas.so
ln -s liblapack.so.3gf.0 liblapack.so

It asked me if I wanted to remove some stuff that wasn't being used, so I said yes and removed it.

Then I installed the latest MyPaint version.

I noticed that when you start the app, it looks like it's loading, then disappears for a few seconds, before finally opening up.