I didn't give up my beloved coffee (caffeine all the way!) while breast-feeding either of my little ones and it never bothered them. They were sleeping through the night by 8 weeks and coffee helped me NOT fall asleep during the day
Although, about a month ago we were on vacation and sharing a room with our kids when my son (2 1/2) started talking in his sleep. He was mumbling and then ever so clearly he said, "wook, Starbucks!". My husband was disgusted that I have "corrupted" my son (obviously my husband doesn't share my obsession) and I was one proud mama!