Not that this will come as much of a surprise, but Google's EMD update, which Matt Cutts announced a week ago, will be an ongoing, periodic update, much like our other algorithmic friends Panda and Penguin.
Danny Sullivan confirmed as much with Google. He writes, "Google confirmed for me this week that EMD is a periodic filter. It isn’t constantly running and looking for bad EMD domains to filter. It’s designed to be used from time-to-time to ensure that what was filtered out before should continue to be filtered. It also works to catch new things that may have been missed before."
Like I noted here, Sullivan says the advice for EMD recovery is pretty much like that for Panda recovery. "After you’ve removed the poor quality content, it’s waiting time. You’ll only see a change the next time the EMD filter is run," he says. "When will that be? Google’s not saying, but based on the history of Panda, it’s likely to be within the next three months, and eventually it might move to a monthly basis."
Google, if you haven't heard, actually did launch a new Panda update to roll out alongside the EMD update, so webmasters have had to deal with both updates at the same time, trying to figure out which one they're actually being affected by. Luckily, the cure is probably the same for both. Quality.
By the way, Google has been making other changes to its algorithm related to the quality of pages. More on that here. There was also another recent domain-related algorithm tweak (in addition to the domain diversity update).