Why is my HD full of nothing? I'm running 10.8.
Everything is updated.
Tried all the usual memory recovery stuff and resets. Disabled time machine.
When I look at at the HD folders in terminal, with show all sizes all the files only total about 110GB (including hidden files)

The only thing unusual about this computer is that it has a ton (~100) of users that are managed with parental controls. Not sure if that would affect this issue. Also, because it would take so long to manually reenter all these users I'm hesitant to wipe it and reinstall everything.

Any ideas before I wipe it and start over? Thanks.
Two things. 


The spotlight process that catalogs files has stopped (perhaps due to low disk space) so they yellow information is incorrect. It should show you a warning IMO that the catalog process failed or needs to update. The "Other" is a catch-all so you're seeing that.
Copy 20 GB of files to an external drive (photo library, movies, virtual machines are easy targets) and then delete them. You can use Finder to show folder sizes and locate some targets. At that point, restart into Recovery and repair the drive and volume using Disk Utility.


Then boot the system normally and let the system run for several hours to see what really is using space. Once you have a good reading, you can add files back from the backup. Your wipe and start over is fine too. Maybe let the system stabilize and show realistic data before restoring your user account and settings/files.

See these for more details:


Why is it important to keep lots of freespace on OSX? What is the impact?
Finder Reports Disk is Full, Other Tools Don&#39;t Account for it