I work a lot with river data. In order for labeling to work well at different zoom levels lines need to be simplified with Douglas-Peucker. It is possible to pre-process the data, but I would need to create separate files for each zoom level I am planning (I am using Development Seed's Tilemill). It would be much simpler to dynamically simplify lines when rendering using Mapnik. There is an example implementation in C++ here: http://www.codeproject.com/KB/recipes/dphull.aspx
Fixed by #2512?
Yes, thanks for helping close old tickets @pnorman.