What on earth? I just noticed this:

1. Turn on the YouTube HTML5 trial (http://youtube.com/html5). You need a modern browser.
2. View a video that supports HTML5 (e.g., Meet the Medic).
3. Right-click and choose Save As in the white drop-down. (Firefox on Linux seems to be able to “defeat” the JavaScript here and gives you the proper drop-down with a legitimate “Save Video As” option; close that and you will see the white YouTube JavaScript drop-down.)
4. You are redirected to Rick Astley - Never Gonna Give You Up.

That’s … pretty weird. And sort of flies in the face of open standards. (It’s pretty much the same trick as when stupid websites in the early 2000s tried to stop you from saving their images by putting a JavaScript blocker to prevent you from right-clicking.)