Fremantle
The latest episode of Between the Brackets is an interview with Tricia Burmeister of the WMF. It's all worth a listen, but one thing that stuck out to me was her mention of the difficulty in creating navigation within MediaWiki where you want people to be able to move between a set of related wiki pages. Other wiki engines, such as Dokuwiki, can do this with namespaces, but in MediaWiki it's normally a matter of a navbox at the bottom or side (the side that's usually opposite a whole-site navigation sidebar).
I've often wanted to divide a wiki up more completely into separate zones by given each their own top-level navigation. The Extension:DynamicSidebar extension helps: it gives separate sidebars per category (the sidebars are stored in MediaWiki:Sidebar/Category:<category>). GroupsSidebar is a similar idea, but separating the sidebars by user group (so good I guess for contributor actions/tool links). I'm not sure what the caching implications are for the above extensions. I might do some more experimenting, and get it working on ArchivesWiki.