It can also be influenced by your HDD. If you have an old, badblock-riddled, sector-relocation-filled, barely alive disk, the write speeds will be ridiculously slow, and so will be FRAPS (as it tries to commit to disk as often as it can, in order to keep the RAM available). I noticed this when upgrading my system HDD (where the fraps recordings were saved) from an old Seagate to a shiny new WD.
