Muck...I have felt your pain bro. I even posted a "Me so Horny" thread over at Chk. 6 during my "trial by pregnancy".
Now...the wife was very generous right up until month 8 of the 3rd pregnancy. Then all went cold.
Baby was born in January. Things are just beginning to return to normal now.....thank GOD.
Now...we were both watching a show once, not too long ago, that stated that the average couple has sex 3 times a week. We (more accurately "I") use this as a guage. If we have sex less than that I make it quite obvious to her that we are below "normal". If more, I just keep quiet.

Our sex life does go in spurts though (forgive the pun). Sometimes we are like rabbits and are at it 6 or 7 times a week. Other times 1 or 2. It is never static.
The wife just discovered "lunch sex" though...which is going to be awesome. Having 3 really young kids has definately prevented us from being able to enjoy sex as much as we would like. The wife is constantly tired from getting up throughout the nights with the baby and then taking care of her during the day, while also cleaning, cooking etc. She also does more than her fair share of work with the two boys.
So, starting this past Friday we have added 2 days a week of lunch sex. Wednesdays (squad night....her suggestion) and Fridays.
She gets the baby to sleep and jumps into the shower right after calling me to tell me to come home.
It is pretty darn cool, I gotta say.
Only thing is....I feel like a glazed donut when I get back to work.