I just experienced a large bout of lag problems, and they have since gone away. The lag started at around 10am PST, slowly got worse until around 1pm, and lasted until about 2pm. It's now 2:22pm PST, and the lag is pretty much gone (in Gridania on Cactuar).

10am to 2pm PST correlates with European Prime Time (That's 7pm to 11pm in Sweden, for example).

So, my question is, when are you getting lag (if you're getting it), and are there times when you have less? If it's primarily during a region's prime time, that suggests congestion (of either the server or some routing infrastructure) as a cause for lag, though there are other possible problems.