Apparently all you need to do to embed a video from YouTube is paste the URL into the content pane. Note, not the embed URL, just the url from your browser window.
Then, the video will be embedded automagically, just like in Posterous I guess.
Here’s a couple of my latest YouTube creations then:
Make sure that you break the links. Just paste the links as plain text (i.e. edit and remove Hyperlink)