A few months back (before it launched), we found out that the Droid X would have limited HDMI functionality - mainly, it would only work in gallery mode. Today, we stumbled upon a new app on AppBrain called Real HDMI that seems to remove that restriction. Check out the item description:
Warning: This only works for the Droid X.
Finally you can enable and disable the HDMI port on your Droid X.