My last task concerning Semantic Media Wiki was to create an extension which adds automatically the "Revision Time" and the "Revision User" of a wiki page in the semantic data.

You can now use these data to sort querries, for example :

{ {#ask: [[Category:Task]]
| sort=Revision time
| order=descending
| limit=3
} }

It's currently used in the Casestudies page of the CC wiki.

You'll find the code and the instructions in the Creative Commons Git repository. This small piece of code is more a hack than a real extension. The semantic properties are supposed to be rewritten in the next version of Semantic MediaWiki, which will enable much easier user-defined special properties.