I'm thinking of it like Amazon's mechanical turk.. where you become enslaved to do work and solve tasks in a virtual world for fractions of pennies in the form of credits you can't pay your rent with. Zero point one star.
Neal Stephenson wrote a novel (Reamde) about pretty much that exact scenario - companies putting mechanical turkish tasks into an mmo-type interface for players to grind out digital currency.
Makes you wonder if Zuck read it and was like "this sounds like a great idea".
This is also reality for some in second Life and wow too. Hence why they are great examples