Interesting discussion over on co.com about this subject:
http://forums.catalina.sailboatowners.com/showthread.php?t=103992
An extremely good reference for system grounding, included in that thread on page 2 is this well written and documented article:
http://www.westmarine.com/WestAdvisor/Marine-Grounding-Systems (http://www.westmarine.com/WestAdvisor/Marine-Grounding-Systems)