I was migrating my files from my old MacBook Pro to External HDD ((Which will be moved back to my MacBook Air)) when I learned this lesson:
Finder is not reliable for moving large or lots of file.
I was copying my iPhoto libraries and the progress was stuck at 80% for hours. I cancelled the operation and copied it using Forklift, and it is done way much faster.
For deleting bulk (and large) files, use OmniDiskSweeper. Don’t even rely on Finder for that.