I have submitted a FAQ to the swish docs that explains how ranking works.

http://swish-e.org/dev/docs/SWISH-FAQ.html#How_is_ranking_calculated_

The FAQ refers to a new feature in the cvs build: RankScheme.

RankScheme lets you experiment with other ranking schemes either via the 
swish-e command line tool (-R #) or via the API ( RankScheme() ). Right 
now there is only one other scheme besides the current default. It is 
explained in the FAQ.

If anyone does experiment with this new feature, we're very interested 
in feedback and examples, as that will help us refine the ranking 
algorithms.

Thanks.
-- 
Peter Karman  -  karman@cray.com