today, my iMac's SSD free space was down to 1GB, and i had no clue why!
i knew that my aperture library was huge (140GB) but i was missing about 30+ GB that i could not account for after doing a "get info" on all folders under my home folder.
so...i figured this might help someone...
i found a folder "iLifeAssetManagement" apparently this is where photostream images are stored.
i had aperture setup to add all my new imports to photostrem, what aperture does is, aside from importing your raw files to your aperture library, it copies the raw file to the asset management folder, so now the exact same raw file is now in two places on my HDD! 
after deleting these images form the photo stream library in aperture, i gained about 30+ gb back yay! of course also turned off the auto add to photostream

