I was aware of the method of installation. As for utility savings, they each give me an approximate percentage but neither will back it up (probably because, as you mentioned, there are so many other factors contributing to air loss).
I have already installed storm doors, new windows (unfortunately sliders which are probably the most inefficient for blocking air), vented and insulated my attic and am in the process of changing the weatherstripping around doors. Maybe I'm being over zealous!
Anyway, I have some references that I can call. Am I correct in assuming that the hard foam insulation boards would be installed over the interior walls? Thanks again for your input!