If I remember correctly, there was a thread that touched on this in the Parenting forum. It may have been somewhere in the long, initial WOHM thread. There were a wide variety of responses, but i think the general consensus was that stopping pumping didn't cause problems for most of the moms re having a sufficient supply when with their child. I, too, was leery of not having enough, and only just returned my pump (I was renting); dd is 22 months old.
How much are you pumping per day, and how many times per day do you pump?