I'm the author of a cartographic library for Python and have been exploring the use of matplotlib and Agg instead of MapServer/GD for rendering map features. It was matplotlib's Basemap module that first caught my eye, and I promised its author that I would keep him up to date with my experiments. For the curious, results are here:
I'm really quite keen on Agg now. Blows GD away for stylishness and seems like it will be fast enough to use in high performance web maps.
While I am primarily interested in programming web map services, it occurs to me that some of the same functionality could be useful to users in a pylab environment. Plotting features from GIS datasets, consuming web map and feature services, etc. If anyone is considering this kind of effort, please let me know, I'd be happy to pitch in.
sgillies at frii dot com