Internally at PlusNet, we make use of Wiki's for storing some of our internal documentation and notes. I recently had to complete some documentation within the Wiki, regarding the new webmail platform that was built.
You might thing this seemed like a simple task, which admittedly, if I was wanting to just do a completely plain text page - but I needed to include some markup, including some internal links, some plain text and some emphasis. However, I was soon to realise that this wasn't the case...
Being someone who generally uses HTML and Forum Software, I'd have expected to have <b> or [b] to make text bold... but no, MediaWiki makes use of '''bold''' to produce bold text. Now, it may just be me, but isn't that rather unintuitive? Given the popularity of Wiki's, maybe it is just me and I'm "set in my ways" given the popularity (and usefulness) of site's like WikiPedia - where many other people seem to keep cope with them fine.