This thread really strikes a cord with me.
I had a short-lived romance with one girl who seemed obsessed with knowing how big I was, once we were clearly on that slippery slope to passionate sex. Now, I'm not big, but she said she wasn't looking for "big".
She just wanted to know how big so she could be accurate with her girl friends. She would stroke my cock and suck the head to ensure that it was as hard and long as it could possibly get. Then we would have an amazing session. It seemed that part of her sexual satisfaction was knowing just how long I was. She kept a notebook of her sizes. It was very revealing about who she had slept with and provided lots of stories, which I found hugely arousing. She would also check men out in public, and say to me, "wish i had my tape measure!" Oh its nice to think back on that relationship.