Been playing a lot more with DocBook at work, and Jon Parise and I have been recreating the incredible phpdoc repository for the Horde/IMP project. It's a pretty mad combination of M4/XML/SGML/DSSSL that combines together and outputs in pretty much any format you would care to name.
Definitely warming to the idea of SGML as a documentation markup language, although I have yet to find a decent editor for markup under Unix (dont particularly like emacs, and vi doesn't quite cut it). Any suggestions anyone? I've heard that XMetal 2.0 is a good one ...