User blog comment:Emptylord/Season 3 - PBE Patch Notes/@comment-89.106.167.109-20121123102646/@comment-5490997-20121123123341

Just go to those item pages and read... If I understand correctly they do stack, but if you have both only 1 will upgrade and for the other the charges will reset. So only if you think you can stack a tear 2-3 times it might be worth it, but I doubt there are many champs who can do that without playing a seriously long game.

Anyway, it's never been OP to get both Manamune and Archangel's, I really don't see how the upgrades will make that any worse. If anything, Archangel's got nerfed because the passive is unique now (ie, Archangel's stacking won't be viable anymore for just raw damage).