I have two DLINK DSM320's kicking around, which I was using before I traveled down the HTPC road.
With LinuxMCE 7.10 Release, the DLink's will see the LinuxMCE uPnp and the MythTV uPnp servers when you search for media servers. This is one of the noticeable differences I've found between the release and the beta's. Before, the DLink's were absolutely useless, but now, I can tell it to use the LinuxMCE uPnp and happily play music, see photos and play back recordings and video, although I have noticed there is lag between the moving image and the audio when playing video, which is one of the main reasons why I wanted to stop using the DLink's in the first place.
I didn't try to connect to the MythTV server. I believe the 0.20 version doesn't do much of anything, but the 0.21 release (of MythTV) does seem to work much better. I can play back everything but my vidoes with 0.21... tv recordings playback just fine, but divx avi movies produce a wrong format error (but as I mentioned above, play fine with LinuxMCE 7.10R's Upnp server).
So I guess they won't be a media director, but if you need to feed a TV with limited abilities, and want something small and quiet, these units could be an option that way.