My friend wants us to breast-feed each other's baby? Is that even safe?

Is there any particular reason for wanting to "exchange" babies? There is a risk of infection for mother and baby in the event of "cross-nursing", which is what your friend is suggesting. Moreover, breastmilk is actually customised for the baby. I would advise against it unless absolutely necessary. http://www.llli.org/llleaderweb/lv/lvjulaug95p53.html