Totem now has API documentation for the API it exposes to plugins. The documentation has actually been in the source code a while, but we couldn't build pretty reference pages from it. Last night, I separated most of Totem out into a noinst library, which we now use with gtk-doc to build pretty documentation. When we make the next tarball release, the documentation should make its way to library.gnome.org for all budding plugin authors to read.
I was all set to copy-and-paste the required gtk-doc sorcery from another module and leave it at that, when I came across this gtk-doc GNOME Goal. It turns out none of the modules from which I would copy the black magic were making full use of recent gtk-doc features, such as namespace support. Another little bit of hacking later, and Totem now has a symbol index which is actually sorted usefully, and will check the documentation when running `make check`.
On top of that, Stefan Kost has recently added syntax highlighting support for code examples to gtk-doc trunk. Good work!
Lets hope other projects follow you on having some decent documentation.
Just because not everyone is a fan of bugging people on the irc :-/