I don't notice a difference in the intensity of my orgasms throughout my entire cycle, but I do notice something else. The day before my period starts is the horniest day of the month for me, then the first 72 hours of my period, I am too busy cramping to think about sex, the rest of my period, I am notably more horny than I am through the other 3 weeks of the month.
I agree, I am always keyed up right before and during my period (though I have never noticed a difference in strength). I believe this occurs because certain hormones are at an all time high (progesterone)and because it is your body's last ditch effort to get you to procreate before you void the ova. Then again that is my hypothesis, nobody is really sure why we get "mid month highs".