I think I forgot to mention it, but people here might be interested in
this project I recently announced:

http://xbiblio.sourceforge.net./citeproc.html

Basic outline is:

MODS + XML citation styling language + XSLT (2.0)

It also supports SRU.

Here's a simple web service demo where the source document is in one
place, and the MODS server is in another:

http://www.ceridwen.com/cocoon/citeproc-0.7/service?source=http://www.ceridwen.com/docbook-test.xml&citation-style=apa-en&bibdb=exist-xmldb&server_url=http://oxfordltgdev.org.uk:8080/exist/servlet/db/mods

... and same document using a different style file, and with CSS
(missing from the above):

http://xbiblio.sourceforge.net./examples/chicago-note-a-en.html

Bruce