I used a doula for my daughter's birth (my only child). While I did want to try to go without pain meds, I ended up getting an epidural because she was face up and I wasn't having any breaks between contractions. The doula and my husband were waiting for me to request the meds - she wasn't pushing me to see it through without.
While my labor did not AT ALL go to plan, the best part of having a doula is the extra support I had in the delivery room. I was never alone, and it freed my husband up to fetch me ice chips, call a nurse, etc. During pushing, I had him to wipe my brow, her to hold one leg, and the nurse to hold the other. In my opinion, a doula is just as much, if not more, for the father-to-be than it is for the laboring mother, since it takes the pressure off of him to know exactly what to do. Actually, having a doula was my husband's idea from the start.