Hi,
One observation that may be related to the rate of creation of new articles: the markup is becoming positively bewildering.
In some ways it's harder than HTML -- just figuring out where the first paragraph is in the markup can be non-trivial. I've had the experience of contributing something, clicking preview, and seeing that I've borked someone's infobox or table or thicket of <ref>s or whatever. To be honest I often will just not submit my contribution, rather than sort out what's going on in the markup. And I'm not a new user; I've been making small contributions on and off for several years.
I can't imagine what a brand new user's first impression is when they click "edit" for the first time... I suspect it's often something along the lines of "eek, I don't want to break this."
I'm certainly not trying to disparage the fine work that's been done to create the Mediawiki software, I'm just trying to simulate the POV of a newbie here (I imagine there aren't many on this list).
- Pat