It would be great if someone could, one day, go through the whole documentation part.
The documentation is not bad, but it is also far from perfect; ruby has a similar problem
by the way. Oddly enough, python has a very good documentation - I am reading a pygtk
book right now and the examples can almost be used 1:1 in ruby.
(One has to adjust
things a bit, but since I know both ruby and python, this is not difficult.)
I think if the official documentation could be improved, I’d try to make it a bit more like
a wiki, allowing user contributions too, and a bit of collecting snippets from, say,
stack-overflow. I’d also visually make the font size a bit larger and easier to read.
Python has some nice documentation as example.
I am also aware that nobody wants to write documentation really, I understand
that, but someone has to do it eventually. 
I think we’d likely also want a self-hosted solution rather than relying on a 3rd party.
This would be good; I think KDE has done something similar to this lately with the
re-design of their website and related parts. There tend to be two main user group
for documentation - the newcomers. They need all the help. And then, the more
experienced guys; they tend to need more quick references only. Right now it seems
gtk/gnome caters more to the more experienced guys, which makes it hard to get
entry into. The higher that initial barrier is, the less likely people go to it. (Qt has a
similar problem by the way.)