Currently portage supports the nicessness only of it's compiling children. It would be nice ;) if also all extraction etc would be niced with the PORTAGE_NICENESS value, as the extraction processes is also part of portage. Same goes for wget etc. E.g. I can emerge -avuD world and go watch a movie, without beeing disturbed a single time. Now, I know right away when a file is beeing extracted because of the stuttering in my movie.
Portage does run absolutely everything at whatever nice level you specify after its first initialization. The problem you are having is related to lack of custom I/O priorities in the kernel. Google for information about anticipatory schedule, CFQ scheduler and time-sliced CFQ scheduler.
There are indeed 3 I/O shedulers hidden under 'blockdevices'. They where all 3 enabled. The problem was much 'simpler' then that. nVidia IDE chipset drivers didn't play nice. Selecting different drivers for the nForce2 fixed the unzipping delay. Thanks anyhow!
