Hi,
There will be more to this article later but for now... Ferret sucks...
If I was to recommend a small-footprint search engine that is fast and EASY to use for Rails I would say install sphinx and use the ultrasphinx plugin. (paginates with will_paginate_on_steroids )
Using Ferret could not handle the initial load when starting 10 Mongrels after a new deployment. Starting 1 mongrel with 2-3 sec wait-time between worked fine!! Maybe I'm doing something wrong?!?