I upgraded to ML a couple of days after the release. It seemed to work fine and the only thing I noticed was that the number of files on my HD went from about 300K to about 900K. I started a plot of the file count and the HD space. After about three weeks I used a utility to remove all non English localizations which reduced the file count to about 750K and also reduced the HD space; still, nowhere near the 300K of Lion. Then the strangeness. Over six days the file count went down to about 280K while the HD space didn't change. Then two weeks later it went back up again and then a couple of days ago it has started down again with HD space remaining essentially constant. I have verified these numbers using Disk Utility and SuperDuper. This is a plot of the behavior I have Googled and found nothing. I assume that since the HD space doesn't change much while the file count changes by about 500K that these are very small files. NOTE: I do not have Time Machine on. Any thoughts?