I have to give some mad props to KDE. About half my main partition was filled with 2 gigs to spare, so I threw Konqueror into "graphical-disk-usage" mode and pointed it at /.
It ID'ed /tmp/kde-tygris as a culprite at 7 gigs and change. It has now been emptied, and now my system's / stands at 45% empty. Of course, /home is on a different partition.