If you are seeing (or rather, not seeing) Facebook posts which aren't getting posted, one possible issue is that Facebook is rejecting the posts due to the content of your webpage.

There is an open Facebook bug which details an issue with their thumbnail selection engine that can result in your posts being rejected by their server.  Facebook does not allow images hosted by Facebook to be used as thumbnails on stories, however their thumbnail selection engine will sometimes select specifically those images when a post is made.  When that happens, the error "(#100) FBCDN image is not allowed in stream" is returned to dlvr.it and is logged in your Destination's error messages (visible on the Destinations tab of your account)

The only workaround for this problem at this time is to select a thumbnail selection method other than "Auto-Detected by Facebook".  Please see this article for more information about our thumbnail options.

UPDATE:

Beginning 2011-02-15 this issue appears to be more prominent, and it's affecting many posts which have no thumbnail at all.  Additional detail has been sent to Facebook with requests for updates.

UPDATE 2:

There has been no response from Facebook to the change in severity of the bug, yet.  We have implemented a workaround by attaching a 1x1 transparent thumbnail (it looks like there's nothing there) instead of sending no thumbnail.  This is allowing posts to continue being delivered to Facebook until such a time as they resolve the issue.