Available here: http://danbooru.donmai.us/pkg/danbooru-1.12.0.tar.gz
And on Subversion: svn://donmai.us/danbooru/tags/danbooru-1.12.0
This is mostly a bug fix release. You can see a list of changes here: http://trac.donmai.us/query?status=closed&milestone=danbooru-1.12.0
I will probably work on 1.12.1 fixing other minor bugs. I will aim for Rails 2.0 compatibility in 1.13.0.