Last modified: 2013-02-23 18:22:24 UTC
Right now it's not enabled as the dependency (Did You Know extension) has not been enabled on enwiki. Since this is only one class, it's not worth it having it into its own extension, esp if this causes deployment hassle leading to it not being enabled.
Moved in https://gerrit.wikimedia.org/r/#/c/43488/
Functionality is described here: https://www.mediawiki.org/wiki/Extension:Did_You_Know