Space issues with Mac Pro OSX 10.7.5 with SSD 120G as boot volume
Funnily enough I also have the same problem now. I don't remember space on my hard drive being taken so much but my 120GB SSD has only 40GB left now too. Using DiskInventory X i know that 40 is taken up by my iTunes library and some other files, but 40Gb seems to have been used by OS. I'm sure it wasn't more than 20 when I installed the SSD.