This is a wiki-fied version of http://bitlbee.org/main.php/extdoc.html (which will be redirected here soon.)
Some other people also wrote documentation about BitlBee. Maybe some of these might be of some use for you:
A project review on FreshMeat.
100 IRC Hacks - BitlBee, from the O'Reilly book.
About BitlBee on AmigaOS (seems to work on MorphOS too).
Short HOWTO in Spanish.
Short introduction to BitlBee in German.
An impressively long BitlBee HOWTO in Hungarian. For as much as I can see from just screenshots, it seems to be a bit focused on Windows, but obviously there's more than just the installation part, so it can be useful for everyone.
And, well, not quite what you'd call documentation, but at least it's written in English and has something to do with BitlBee, some speeches/ramblings by Sjoerd: