^What these guys said. However, when going through and deleting old things of mine, I went into "Library" and mucked around in there, deleting things for 'KNOWN" programs that I knew I uninstalled.
By known I mean, it blatantly has a name of (FireFox, Safari,) or something like that. I never went past the library folder and definitely didn't mess with permission files.
If you want to get a couple of programs that help show the load on your hard drive, Disk Inventory X is a free one that I use... DaisyDisk is a better looking but pricy option... I think it's 10 bucks on the App store right now (sale or something). \
Oh and get a program that deletes the system preferences of a program when you delete the application; I use AppCleaner. It's free and it gets the job done.