I'm not sure exactly how the script works but I recently found out that the flash files, which are normally stored in /tmp until you download/watch another video are now deleted or shadowed after they are downloaded. Checkout the script flashcache
Once you have completely buffered a flash video (not just Youtube videos), run flashcache
. Just do this:
chmod +rx+rx+rwx flashcache
then copy it to your /usr/bin/ folder. Then you can run it like any other script/app from the command line.