xmpsync: a command line tool which adds XMP star rating to SmugMug
Well, not quite. It maps XMP star rating from local JPEG files to tags on SmugMug, which can then be used in smart galleries. There is a number of feature requests for similar functionality (http://feedback.smugmug.com/forums/17723-smugmug?query=rating), but no solution from SmugMug so far.
If you'd like to be able to organize your photos in SmugMug by XMP star rating, are not afraid of command line or immature tools, then you may find this useful: https://github.com/paterczm/xmpsync. It does help me with my photo publishing workflow.