Delta made an announcement on January 17, 2013, about the changes to its SkyMiles program starting on January 1, 2014 (read more here).
Starting on January 1st, 2014, Delta added a MQD requirement in addition to flow miles to reach Silver, Gold, Platinum or Diamond status with the program. The MQD requirement is not onerous for those that fly on mixed fares, but can be problematic for passengers that always fly on rock bottom ones.
The MQD requirement only applies for SkyMiles members residing in the United States.
You can now easily see the MQD amount by logging to your SkyMiles account and choosing My SkyMiles Summary. My MQD amount is zero, as I have not had any Delta plated tickets this year and hardly any flights on SkyTeam airlines.
The MQD requirement will not have such a huge impact for other SkyMiles members than those that always fly on the lowest fares. Most passengers fly on mixed fares and will easily meet the MQD requirement.