Following bug #147466, I am filing a new bug. The matplotlib-0.87.7 recently updated in the main tree could use a lot of the features and patches from the gentooscience overlay one. It also needs at least a numpy-1.0 (but see the ChangeLog in the overlay for other). If the gentooscience web does not work, layman -a science && layman -s science will.
matplotlib-0.90.0 in cvs now implements some of those features.