A similar problem has been asked before, but the situation is different and the solutions outlined in the thread did not answer my questions. I have an Early 2008 (meaning last model before unibody) 15" 2.53 GHz MBP. I cleaned up my computer and its 250 GB HDD (50 GB Boot Camp, rest OS X), repaired permissions, did a full back-up to an external hard drive with a total of around 9+ GB free on the OS X partition. I downloaded Lion from the App store, brought me down to about 6.3 ish GB. I attempted to install, Lion said no because of the way my BootCamp partition was set up, I said fine, I'll wait till I get a new HDD and set up a clean install then. I didn't manage to take a look at free hard drive space at the time. Later that night, I went to back up/sync my iPad. It had been a while, but my iPad hadn't accumulated much data. It was also time for an update. As the update was unpackaging, I got the message that I'm running out of space. I had gone from 6.3 GB to 100 MB. I hoped it was just the firmware update unpackaged, but after the update went through and I restarted, I had only gotten back to 1.2 GB. I woke up the next morning to have 800 MB, which slowly dwindled down to about 600 or 500 MB. I when to the root which had OS X Lion Update Files folder for about 3.7 GB, which I ultimately deleted, but none of the space came back even after a restart. What's going on? I've already looked through files with OmniDiskSweeper, which said I have used about 177 GB, meanwhile my hard drive reports 195 GB used, which makes me think my hard drive drain is in hidden folders somewhere. EDIT: Just repaired permissions again, no change.