In case you don't know of this way: I download YouTube videos by starting a video on its YouTube page, then clicking on Activity in the Window menu in the topmost Safari bar. This opens an Activity window with a list of active items; the one that is the biggest size I copy; then clicking on Downloads in the topmost Window menu, in the blank Downloads window that then opens, I do a paste. This pastes in what I have copied from the Activity window, and begins downloading the YouTube video.
There is the Free iTube Grabber which can capture almost any audio and/or video stream (it says here) but only works with Intel Macs.
Firefox Download Helper is also supposed to work, you have to be logged into YouTube first.
and the RealPlayer Downloader that comes with RealPlayer SP for Mac from:
which also downloads videos from YouTube.
There is also iTubeX which allows you to download videos (Flash, HTML5 and others), .mp3 and .swf files from almost every website as easily as possible:
Lastly: How to download Flash videos and play them in Quicktime using Perian is explained here:
It's the video at the bottom of the page.
Last but not least (as some of the above may not work with Snow Leopard or Lion) there is the 'pwn trick':
For example, the full youtube site for your movie is:
As soon as the movie starts, pause it and add 'pwn' in front of the youtube part of the url so it looks like this:
Hit Return and then follow the instructions.
For some reason the Activity window doesn't always work. You can see the file but then clicking it only opens another window that only plays the content without allowing you to download. I started using "Fastest Youtube Downloader" and found it simple to use. A few weeks later I purchased the Gold version and have been satisfied.