I'm a psync user too, and know the symptoms that you're talking about. Every so often there's a directory that refuses to die. I think there are a couple of possible causes of this behaviour.
(1) a directory contains links to "deeper down" in the hierarchy. So the order of deletion of items must be implicated here (or at least the link-following behaviour).
(2) I added ".DS_Store" to the list of files to ignore. (You can do this within the "psync" file itself; it's a few screens down from the top.) This is fine except for targets that already existed on my image volume with .DS_Store files in place. Because I've instructed psync to ignore them it doesn't delete them from the target, and the directory is consequently non-empty and not deleted, even after deletion from the source volume.
They're the only two difficulties I've run into: apart from that it's been full speed ahead with psync.
Cheers,
Paul