Positive GMPC experiences?

[Lord Torath]

My definition of a GMPC is a character that the GM considers "his PC". He actually has some personal investment in the success or failure of this character different from all the NPCs that he also runs, in that he is doing well if this character does well, and doing poorly if this character does poorly.

This is pretty much how I see it. Anything else is some flavor of NPC.