I just started playing with Disk Inventory X, a nice treemap diskspace visualizer for Mac OSX. (Windows users can use the older and more complete WinDirStat to do something similar.)
Disk size has nothing to do with importance, but I still get a weird feeling seeing my music collection as a big blue block some 50 times bigger than the project I’ve been working for almost two years. Now I wish I had a treemap for how I spend my time during the day…
Update: and for Linux there’s KDirStat, which is apparently older than either of the other two…