It's interesting, I never felt a letdown with my second baby, and couldn't pump more than half an ounce. I felt multiple letdowns with my first and could pump 9oz. in 15 minutes.
This time I only feel a letdown while nursing, but never while pumping, yet I can still sometimes pump 1/2 an ounce with each squeeze with the Avent Isis hand pump, or at least 4 oz. in 5 minutes.
It's weird how it can be so different each time! :
I have had different experiences each time, as well. With DD#1 I never felt a let down. I was able to pump enough to keep her EBF, but it was a struggle at times. Now I'm a milk making machine! LOL I can pump 5 oz in about 5 minutes, usually. I experience a very noticable let down now, as well. Not so much when I pump but definitely when I am nursing!