I've been running PMS now for over a year and have had no problems with the Metadata agents pulling down both TV and Movie coverart and descriptions.
Since I've updated to 0.9.8.10 I've had the problem that no metadata is downloaded for my TV and Movies. I'm not sure how to correct this - even if I do a manual lookup (Fix Metadata) it doesn't work.
I just noticed the same issue today. I'm on a Mac and have no issues until today. When I go to Agents, nothing is loading. Also takes a very long time to try and adjust any settings.