What are some advantages and disadvantages of doulas?

Having a doula at your birth can result in shorter labors with fewer complications, reduce negative feelings about your childbirth experience, reduce the need for pitocin, forceps or vaccum extraction and cesareans and the mother's request for pain medication and/or epidurals. Women who have doulas present at their births are more likely to have successful breastfeeding relationships, and are less likely to suffer from postpartum depression.

I honesly can't think of a disadvantage of having a doula at your birth, unless you have a negative relationship with your doula. It is essential that you find someone that you feel comfortable with and supports the vision you have for your birth experience.