Following my considerations around virtual money and social networks (especially Facebook), I've come across an interesting question (is Facebook a virtual world?) and a meaningful thought about a way to measure engagement: the quantity of uproar from users over interface updates and changes and, at the same time, rising awareness of concerns regarding "digital citizenship".

Back to the original question: being a superimposed layer over reality, I would call Facebook neither virtual nor world and I agree with the author of the post. But, in order to decide this issue, we need a definition of virtual world and the two I've found (by Richard Bartle and Mark W. Bell) are far from satisfactory in my view – missing the point as to defining why we should call the environment "a world" instead of "a digital interface". After all, if we ignore subtleties about profiles having agency beyond their creator and what "world physics" are about, there is nothing that prevents us from considering a corporate intranet as a virtual world and a username as an avatar…