I shall tell you my secret
UBERLAG - A phenomenon in FFXIV characterized by an unplayable level of "rubber banding" of characters and the repeated freezing and fast-forwarding of on-screen action.
So I think I've stumbled onto the reason for Uberlag. Or at least one reason that affects me.
LODESTONE.
I noticed a pattern the other day. On every occasion where I've gone home and experienced that sort of lag, ruining my night, it has always been on the same days that I've made forum posts on here. Just as sort of a "nah, couldn't be..." test I tried logging into the forums from my computer and then booting up FFXIV on my PS3. After a few minutes the lag was ungodly. I couldn't tank, couldn't heal, the instances were totally unplayable. After an hour of that BS, I went upstairs and logged out of the forums completely, and then reset the PS3 and logged back onto XIV. The lag was completely gone. I successfully tanked Pharos Sirius as WAR without a single issue.
I went upstairs and logged into Lodestone from my PC again. About 5 minutes later, everybody started teleporting and rubber banding around in RevToll. Logged out of the forums and the lag was gone a few minutes later.
Since the Lodestone and forums are tied to your character data, I have a theory. That any time you are actively logged in to the Lodestone, the system is constantly "pinging" your character data to keep your profile updated with your current gear, level, appearance, face for forum avatar, etc. And that this separate connection to your character information, at the same time you are USING that character in the game, is the cause of Uberlag.
So if you're lagging like hell, make sure you're not logged in on the forums or Lodestone anywhere, restart your client, and try again. Lets see if this is really a thing.