I just set up this blog with PyBlosxom. The installation was completely smooth, and it was trivial to get the style the way I wanted it (like the rest of my website, that is).
But getting XHTML 1.1 compliance took a long time, because of of the Content-type header. I ended up having to write a plugin, which meant learning how PyBlosxom renderers.
My default flavour is called adam; with that in mind, here is my plugin: