Without comparing every file the most striking difference is the Stack Overflow dump, where the current 012011 Stack Overflow.7z has only 934MB in contrast to the former Stack Overflow 11-2010.7z with 1.83GB.
My initial thought has been, that the deletionists might have finally won ;) But introspecting the former yields two missing files in fact, namely
posthistory.xml, which are still present in the other sites archives (haven't checked any single one though); in addition
comments.xml is an empty file, so all in all the integrity of the data seems a bit questionable.
Could the dump get fixed and rerolled accordingly, especially in light of the (somewhat surprising) shift to a bi-monthly release cycle? Thanks!