I recently purchased a 17" C2D MacBook Pro with 2GB RAM and the 160GB HD. I noticed that I did not have as much free space as I thought I did so I went investigating. This lead me to downloading WhatSize and running it. It, as well as OSX tells me that I am using about 97 GB, but when I add up the size of the folders and files on my HD in WhatSize, I find that I am only using about 53 GB, if that. Why might this be? Seems curious to me.