A week later, I broke down and bought it, especially since my girlfriend and I had been having some problems budgeting quality time. Now, we can't get enough of Sex Flex. We've worked our way through all of the exercises - and we've even made up some of our own. (If the authors are interested, they can contact me at the above e-mail address!)
Thanks to the authors for their great info and the solid base on which to build new exercises. My relationship's the better for it!