If you're using from matplotlib import rc and rc('text', usetex=True) and savefig(filename) you need dvipng installed. This isn't installed automatically. Maybe there should be a 'tetex' use flag or something like that, which installs dvipng if it's set. I had tetex installed already and execpt for dvipng I didn't have any problems. However, I couldn't find any dependenies regarding tetex using equery. Maybe tetex is also needed together with dvipng.
fixed. Thanks.
Please make this dependency on dvipng optional (USE flag), because more than 100M sources of tetex is too much for me...