James, Joebuck has a good link about measuring FOC. If you go to the Tradgang Archives and look for the reports of Dr. Ed Ashby
http://tradgang.com/noncgi/ultimatebb.php?ubb=forum;f=24 you will find more information. It will take time to get through it all but it is facinating IMO.
Briefly, Dr. Ashby has done many years of research on the effect of high FOC on penetration including info on heavy bone breaching, broadhead viability, etc.
While many will argue that it makes little difference for them when hunting deer sized game, with a well tuned bow/arrow combo, the facts remain that high FOC is a way to optimize your set-up.
Like JoeBuck, I too drink the koolaid.