I know this is an old thread, but I wanted to add to it in case it helps someone else.
First of all, thank you, the Disk Drill tip was helpful.
I was getting 'out of memory' messages and things would lock up. There were several things that were going on:
1) The Disk Drill issue was keeping the space from freeing up.
2) The sleepimage file was quite large - which normally wouldn't be an issue, but it was so out of space I needed to free it up for a few minutes just to be able to move some files off the drive. It got rebuilt later on. (I deleted the sleepimage but people have warned not to touch the swap files, so don't).
3) Most importantly: This is basically for editors, but the main issue on my drive was that in Premiere, my preview files were set to an external drive, but the cache files were piling up on the hard drive in a hidden file (in Mountain Lion). 400 gigs worth (lots of previous crashes until I found the issue, which fwiw happens to be it doesn't like open audio waveforms in the timeline, so close your tracks unless you have to open them to make changes). Anyway, I thought I had deleted my cache, but it was piling up on the hard drive in the default location: home folder/library/preferences/adobe/common/media cache files. So it was filling up as fast as I could delete space.
It seems that cleaning the cache from inside Premiere didn't help much - maybe this was due to the cache files from the other crashed projects, not sure.
If this is your issue, go in through the finder, delete your cfa and pek files if they are left over from other projects, and let Premiere reconform your files. This freed up 350 gig of space.
Google how to get the hidden library file to show, someone can probably tell you how to do it, I don't recall what I did. But I did make an alias of the library folder to make it visible and easier to get to, and also stuck a shortcut to the media cache in the finder sidebar to keep an eye on those files.
Omni Disk Sweeper was the hero in helping me find the culprit.
Hope this advice proves useful to someone.