Many thanks to everyone who replied to the Internal Control Index Survey. I've posted the results to the ICI page of my Wiki, and I can send anyone the raw data if they are interested. http://fellrnr.com/wiki/Internal_Control_Index#ICI_and_Running_Survey
I updated the Wiki page to give a few details on how to interpret ICI values. I hope to have more information once some inter-library loans and book purchases arrive.
Sorry this has taken so long, but I had to find the time to write some code to scrape the data from the Survey Monkey site, as you can't download the data without a paid account.