Psych

I just watched the episode on Hulu(great place btw).  I think Yin is either Mary's son(if she had one) or a past pupil of Mary's who was very jealous of Shawn as a kid.  It seemed that picture shown at the end of the season ender was Mary and a young Shawn.  Shawn is still the basic kid in a adult body using his smarts to snow people(most people who don't really know him).  JMO though... there are alot of ideas thrown around the comments section for that episode on Hulu. 

My friend said she thought that picture was of Yang and a young Shawn too.  I didn't really look at it closely enough to tell but with Shawn's powers of observation, is it really possible that he knew Yang as a child and didn't remember?

I love Hulu too.  I looked for the comments you mentioned but couldn't find them.  What I did find was another site that had everyone from Henry to Gus being Mr. Yin.

My personal favorite:  Mr. Yin is The Mentalist. LOL