Please see the "Special Code Legend" (to the left of the text-entry box when you create a post) for instructions on embedding You Tube clips into your posts.
I inserted a couple of videos in another post and they showed up at first, but have now disappeared leaving a blank space as well. My browser status keeps saying it's waiting for items to load and it's taking a LONG time for them to show up if they do at all. New feature jitters I guess.