The Code Style documentation is now available from the main website in the documentation section: http://www.inkscape.org/doc/

While we can consider it official enough to start using in updating the code, this document shouldn't be considered cast in stone. Discussion about updates and changes to the code style can continue to be done in Wiki as before, and as concensus is reached on changes, the formal document can be updated as appropriate.

http://inkscape.org/cgi-bin/wiki.pl?Coding_Style

Bryce