I'm bringing my machine to the Apple store in three hours to get my HDD replaced and I want to make sure all personal files are wiped from the machine before I leave it with them. Last night, I created a new Admin and then deleted my previous user account / profile through Disk Utilities. Took nearly ten hours to securely erase everything (nearly 500gb of files). Problem is, if I hit "about this Mac", it still indicates that only half of my 1TB drive is available, so it appears that all of my files are still on somewhere this machine! What can I do?