Just want to add my two cents in that I too have been having major lag problems during the last several months.

I am on the East Coast, USA, Primal Data Center. I connect to the Montreal server with Verizon FIOS. And during peak game hours, around 7-8pm, I get moderate to severe lag issues. Slow ping and packet loss.

Tracing the packets determined that there was a hop somewhere after NYC that keeps dropping packets and thus causing this lag. Verizon can't do anything about that router. I hope that Square Enix will.