This is a problem in Internet Explorer only.  If you try to embed a youtube video, IE tries to render the video on the edit page and throws a javascript error that prevents the page from being saved again.

Here is an example of some code that was trying to be embedded.

<p>View the trailer of Karabey's film, My Marlon and Brando, below:</p>
<p><object width="425" height="355"><param name="movie" value="http://www.youtube.com/v/r02zbifnOzA&hl=en"></param><param name="wmode" value="transparent"></param><embed src="http://www.youtube.com/v/r02zbifnOzA&hl=en" type="application/x-shockwave-flash" wmode="transparent" width="425" height="355"></embed></object></p>