When I run across video clips I think are interesting I often do so in a bunch, but rather than dump them all onto the blog at the same time I take advantage of a WordPress feature that lets me schedule them to appear later. For some reason, lately that seems to result in the loss of the XHTML code that embeds the video in the post. I'm apparently not the only person experiencing the problem. See for example this discussion thread.
I have tried to go back and re-insert the code once the posts have appeared, and this seems to work. So if you want to see any you might have missed, scroll down and (I hope) you'll find the missing links restored.by