No space opened up after moving 30GB to external drive

[Djarr]

The hard drive on my MacBookPro is completely full, so I moved 30GB of movie files to an external hard drive (dragged and dropped while holding whatever key makes the 'plus' go away). The files copied over and disappeared from my internal drive but the 30GB didn't open up. What did I do wrong?
I emptied the trash (even though I shouldn't have to, right?) but still no space freed up...

 

[satcomer]

Download the program Yasu and run all the cleaning routines. Let the program reboot your Mac and upon that reboot manually reboot again to completely rebuild your startup/shutdown cache. This should help.

 

[pooky]

It's quite possible that the extra space was used for swapping. Your drive might have been so full that the OS didn't have enough for virtual memory. You freed some space, and the OS gobbled it right up to use as swap space.