I installed iStat 2 days ago and just yesterday I noticed that my HD space slowly decreases; not by a lot. For example, yesterday it said that I had used only 12.06 GB of space. A little later it said 12.07 GB and then 12.08 or 12.09 (I don't remember which one). Today it started in the low 13's and then it went to 13.07 and then 13.09. Currently, it's at 13.17 GB used. Why does it do this? I'm not saving any files, pictures, videos, etc. I'm just on Safari and listening to Pandora and browsing.