The MetaCrisis Doctor was a full regeneration. "10" was shot by a Dalek and started regenerating. He didn't want to change, so he concentrated the energy to his severed hand, since it has his DNA. So, Matt Smith's Doctor is the 11th Doctor in his 12th body, in his 13th life. Confusing, isn't it?
River Song used her remaining regenerations to revive the dead Doctor from the poison she gave him from the Judas Tree, which prevented him from regenerating. Now, nobody knows if a Time Lord/Lady could receive extra regenerations from anyone other than the High Council. My question is doesn't he still have the poison in his system, and if he does, should it still prevent him from regenerating?