Every time I have to use MediaWiki markup ("wikitext") I wish it supported any flavour of markdown instead.
@liw Sometimes I have similar feelings, but actually I'm not sure Markdown would be a good option for a wiki like Wikipedia. First, links work differently and [[link]]ing like this on a wiki is very convenient (especially for languages that have a lot of declination). Second, markdown is pretty minimalistic and yet sometimes verbose (say, image nested in an anchor with an alt tag can be visually confusing to parse). Then, ordered lists... I'm not sure.
Lars and friends