Hi kids I found some useful info about Refineries that I'de like to post.  I found this in the planet entity files where it lists values for extraction rate and a value for "Refinery Rate.'  For example :

A refinery ship boosts an extractor's production rate by .06  (.08 for netural extractors).  Each refinery can build up to 10 refinery ships.

For reference, a normal extractor (at full allegiance) produces .4 resources/time interval.  (.53 for netural extractors) 

So... if you're refinery is servicing say, 6 asteroids (which seems about average) it is generating about as much resources as a claimed neutral extractor.  Not too bad if you ask me, especially later on once your economy can really afford to build those things.