The official forum went mad with activity from irate users yesterday, as Uplay servers went down, affecting all games using this login - including but not limited to Heroes VI.

Kotaku also reported on this issue.

I personally think this is yet another sign that making games too dependent upon online connections and company servers is a strategy doomed to fail. It is a sign that the game companies cannot keep their end of the "bargain"; keeping their online resources active constantly so that players can ... well, play. I.e: get the product they have paid for.