i won't read the other messages here so i don't get influenced by their content.
this is my very own experience and the way i see it happening, no scientific back-up or anything like that:
in my case pregnancy made my breasts considerably bigger which led to strech marks and drooping (they are now very low as compared to what they used to be). having returned to their previous size after finishing breastfeeding, i assume that the estra size meant the skin streached and it didn't go back to it's original size itself, but the inside did (hard to explain) hence empty sort of breasts hanging down.
the texture is not the same either, they are not firm as they used to be and i think this might be due to constant changing shape during breastfeeding (full, empty, full etc)
looking back i think if i did not breastfeed, it is a very good chance they would have maintained their fullness.
they would have still gotten lower and strech marks (i'm sure that happened during pregnancy)
and pregnancy itself makde the nipples much more visible, they are now dark but breastfeeding seemed to make them bigger too, sort of streched outwards and also permanently hard (deffinetly that's the breastfeeding).
all in all my breasts are completely ruined and i used to love them before, one of my best assets, all gone for eternity...
if i coud turn back the time to start again from the beginning i would not breastfeed again. but that's me and i know lots of people would totally disagree with this statement.
btw, i breastfed for 1 year.