Caddie, my breasts never felt full during pregnancy although they did leak occasionally. Your milk doesn't come in until after the baby is born so the bahaviour of your boobs during pregancy doesn't indicate how sucessful you will be at breastfeeding. Some women never feel a let-down - its not nessescary to be able to feel it to breastfeed sucsesfuly.
I would really recomend that if you're worried about breastfeeding that you look up the ABA website and read some of thier articles and maybe attend some of thier preparing for breastfeeding classes. They cost about $70 which includes a subscription to thier magazine and free attendance for your partner/support person. Its much easier to learn about breastfeeding while you're pregnant than in the days following birth when you're a bit overwhelmed with your new baby and recovering from birth.