Thanks, very useful! Any idea whether we can expect an improved import algorithm as this seems to be a serious bottleneck?
For full planet import, if you have 8+G RAM (as you should have), then I strongly suggest to set -C 8000. Otherwise it will run out of memory and will be significantly slower. Currently (as of Sept'2010) actual memory usage is about 7GB (in slim mode).
See also much more in http://wiki.openstreetmap.org/wiki/SotM_2010_session:Tuning_the_Mapnik_Rendering_Chain about it