A lot of comments have been made about whether wiki markup is a barrier to entry, and if it is, whether it (the barrier to entry) is a good thing or not.
On the first part, it would be interesting to measure edit attempts - how many people clicked edit, but did not click save or preview. Of course this does not tell you if the markup is a barrier to entry, but it may be some kind of rough indicator. The experience of editing a well developed page can be like looking at source code: if you don't know the language, there's an awful lot of gobbledygook in there, and I'd think it intimidates some people.
So... it would just be an interesting figure, to hold up next to other figures, like completed edits.
Aerik