I have simmilar issue. Diskutility reports that i have 93GB used
But when i try to find what is taking this space and run Disk Inventory, i get results that
i only have files for 64GB. Where my precious 30GB are gone? that's like 1/4 of my total
capacity on my air (120GB)
I have run disk utiity if found no errors. Some time ago i had similar issue, but then disk utility found
problems and fixed them so i got my space back. But not now.