translatewiki.net, it says "Powered by Semantic MediaWiki". It means that not only is translatewiki.net where you can localise Semantic MediaWiki, it is also a place where semantic web approaches can be used in earnest.
As translatewiki.net is a production environment, I do not feel comfortable to start experimenting wildly. It is however one of the more visible and strategic places for Semantic MediaWiki to pop up.
It is the closest you get to the real thing; implementation on Wikipedia itself. So my obvious question is: what should we do semantically on translatewiki. Who will provide us with the ideas that will show off the brilliant functionality that has now become a possibility?