When I realized my home directory had almost 200GB, I had to figure it out. 3 minutes later, I found that ~/Library/Application Support/SyncServices/Local/save.isyncplayback was close to 180GB…bingo, there is it.

A quick Google and some link following had me to the Apple Forum topic: Save.isyncplayback folder eating my hard drive in no time. A few months ago, I had been trying to figure out a Plaxo/iCal sync oddness and must have turned on verbose debugging. Turned it off and cleared the history… I’m a happy camper again with plenty of disk space.