Yes, all comments and solutions (above) were correct - in the end, the filesystem was corrupted like I suspected.
The solution was to boot up with the INSTALL/BOOT disk, and run Disk Utility. Inside Disk Utility, I simply had to select my Hard Disk (they're listed by name), and then click the "Repair Disk" button - it scanned for a good 1.5 hours, and fixed all the errors, including restoring my Dev/Null folder.
I saw a lot of different instructions in online forums about how to boot up directly into Disk Utility - including "insert boot disk into drive, turn computer off, when re-booting, hold down the "C" key, and you will enter Disk Utility!"
ACTUALLY - that didn't work for my OS X 10.6.6 - I instead had to boot up with my boot disk, enter the OS X Install screens, and you can find the "Disk Utility" program in the "Utilities" menu.
Here are the steps- this works for any/all maintenance you want to do on your OS X 10.6.6 Filesystem:
NOTE: these are only instructions to repair your MAIN HARD DISK that you usually use to boot up. You can't repair this disk when you're running OS X, so you'll need to re-boot into your BootUp Disk to do the repairs. To repair any/all other disks, you can simply go to UTILITIES>Disk Utility, select the disk you want to repair, and click the "Repair" button.
TO FIX MAIN HARD-DISK (main boot up disk):
- Insert your OS X Disk into the computer (it could be your original OS X CD, or a USB key loaded with a copy of a OS X INSTALL disk.)
- Turn computer off.
- Restart computer while holding down ALT/OPTION key during boot-up, keep holding it until you see a screen that lists the different "boot" hard disks and/or USB keys currently plugged in to your system. In my case, I saw my installed Hard Disk (the old one I want to fix) and my OS X CD, which the system recognizes as a boot disk too.
- Click on the CD (or USB key).
- It will take 30secs to a minute, but your OS X Install screens will open up - click on the language you want (English in my case) and click continue.
- BE CAREFUL - in the next few screens, you don't want to click on "Install" or anything similar -you should now see a new MENU BAR along the top of your screen, with a menu called "Utilities".
7.Click on "Utilities" and select "Disk Utility".
- Now you're inside the Disk Utility program - simply select the Hard Disk you want to repair, and then click on the "REPAIR" button. It'll take an hour or two to scan and fix everything, but it should work!
When that finishes, click to CLOSE the Disk Utility program. I couldn't find any way to restart the computer, so I just held down the power button, and then again to re-start. Don't press anything and the computer should reboot into your main OS X install (hard disk) with no problems.