Just wanted to post the latest fix for this that I figured out:
The latest version of XBMC's 'useragent' field has changed to 'Platinum' in reference to it's latest codebase.
Just change the useragent in the XBMC.conf file in the 'Program files\PS3 Media Server' folder to read (with Notepad, etc. - and must use Notepad with 'Run as Administrator' if editing from Vista/Win7:
(instead of 'Neptune')
And save XBMC.conf and restart PS3 Media Server.
XBMC is now detected again as a 'XBMC client' and I can see all my video files including my 'Videos' folder that I could not see before - and all videos play fine.
XBMC is an awesome DLNA graphical client that you can use to test your PS3 Media Server config - and I highly recommend it: