Nipple Confusion

"Breastfeeding and bottle-feeding require the baby to use their mouths and jaws in ways that are completely different from one another. When a baby is first born, it possesses a suckling instinct that is natural to breastfeeding. If a baby is first fed with a bottle, not only will the baby have to endure the process of gastrointestinal adaptation to the unnatural composition of formula, they will also have to go against natural instinct and learn how to get milk out of an artificial nipple. "

- From "Common breastfeeding concerns: nipple confusion"

Bottles and pacifers can both cause nipple confusion to babies. Even if the baby is able to determine breast from artificial nipple, use of artificial nipples can weaken the baby's skill at Latching On and cause breastfeeding difficulties. It is very rare that a baby needs formula immediately after birth, and in situations where nursing is very difficult because the baby is premature or there are maternal complications, there are Bottle Alternatives For Babies Who Can't Nurse that will not force the baby to "unlearn" its natural suckling mechanisms that way that artificial nipples will.

Other Sources:

"Nipple Confusion" - AskDrSears.com

"Nipple Confusion" - Breastfeeding.com

Also See:

Cluster Feeding

Increasing Milk Supply

Good breastfeeding from day one

Supplemental Feeding