I have been using the youtube totem plugin a lot lately, and I think it would be useful to have the possibility to use it to save videos to disk. It already seems to copy the actual video to /tmp, so I guess technically it shouldn't be too difficult.

You already get a menu when you right-click the videos in the sidebar, so it would only be a matter of including a third menu item, "save to disk", which would span a save dialogue.

I'm attaching a mockup.