It occurred to me that Jason Thorpe wrote in gmane.os.netbsd.devel.kernel:
> If we're going to do this, we should actually document this stuff  
> using Doxygen's special comments format.

That's my main issue with Doxygen. It's all very nice, but it requires 
special comments to be really useful. Without that, it barely exceeds
cscope-based stuff.

Adding to this, Doxygen needs graphviz to be useful, and graphviz is
surrounded with problems.