well i have done it for 4 hours but my wife was dizzy for 3 days it just will make your woman mindless i dont know if it is worth it any ways but its fun to do.
i got this book
http://www.amazon.com/Tao-Health-Sex-Longevity-Practical/dp/067164811Xit is a must read if you want to have great sex its mostly for men to controll themselfs but it will explain how to keep things going for hours. if you put into use the principles.
The Tao of Health, Sex, and Longevity
read it and learn
<img src="/~stretch/ubbthreads/images/graemlins/tongue.gif" alt="" />
although i am no longer married and so makes this knolege worthless.