Return of the Boltzmann Brains
  Linde in hep-th/0611043 shows that some (though not all) versions of the global (volume-weighted) description avoid the "Boltzmann brain" problem raised in hep-th/0610079 if the universe does not have a decay time less than 20 Gyr. Here I give an apparently natural version of the volume-weighted description in which the problem persists, highlighting the ambiguity of taking the ratios of infinite volumes that appear to arise from eternal inflation. 
Don N. Page