Blizzard announced today that they have fixes incoming for the latency experienced in Naxxramas and Northrend. These zones have caused some unexpected lag recently, and Blizzard is well aware and are prioritizing a fix. Here's the full announcement.

For the last several weeks, our players have been experiencing periodic latency in both outdoor Northrend areas and Naxxramas, and we wanted to provide you with several updates on what we're doing to resolve these issues. As many players have discovered, the outdoor Northrend latency has been tied to activity in Wintergrasp. We are actively working on a server-side fix that should address the high latency experienced in the outdoor world when Wintergrasp is active. This fix is currently in testing on internal test realms and we anticipate that we'll be able to push it to live realms in the near future. Concerning Naxxramas, optimizations are being made that will address both the latency and disconnection issues affecting players while in that zone. These optimizations will be included with the next minor content patch.

We appreciate your patience as we work to address these issues.