Two of the largest Cataclysm servers in EU have 99% horde, and 99% alliance dominated populations (see ironforge.pro for statistics). The same is true for US.
This will likely continue into MoP unfortunately if nothing is done to address this issue. Did Blizz announce anything for MoP to balance this?
PvP servers shouldn’t be sitting at 99% faction domination, it kills the purpose of a PvP server entirely where it essentially becomes a PvE server.