Browsing through the "New Springerlink", I came across Gravity, the Inside Story It's got some interesting, though non-classical, points about gravity. The author starts out with an argument about the inevitability of horizons. This is sort of amusing considering the amount of angst we appear to be having currently at PF about the mere existence of event horizons. But that's not the main point of the paper. and The author argues that it's not possible for horizons to have a temperature without some sort of microstructure in spacetime, even if we don't yet have a theory that gives said microstructure. The really interesting stuff happens when the author writes expressions for the entorpy S_matter and S_grav, the entropy of the matter fields and the horizons - and derives Einstein's equations as a low order approximation to the maxmization of entropy, There's also some higher order terms which make the theory depart from the simple action of GR.