I, too, can report partial success with the MediaSmart client. I had to set the TCP/IP port for the UPnP server, then add it to my Windows Firewall exception list. Once I did that, I was able to see my playlists and stream audio from my MC server.
I can't seem to see album art, nor can I see thumbnails of images I am displaying. Once I select an image, I can see the full sized one just fine, but can't see the thumbnails. Any suggestions? I store most of my music as .ape files, which must be converted to .mp3 files. Even if I play native .mp3 files, I cannot see the album art. Any ideas?
Overall, I like the MediaSmart client box. It is small, stylish, and absolutely quiet. The UI is a bit sluggish, but I can live with that.