I had a doula during my pregnancy and labour and it was a great experience. I wanted a midwife but due to medical conditions they would not accept me as a patient so I opted for a doula instead. I gave birth in a hospital and I really found that a doula was helpful as they are supportive during the entire experience as the nurses are often too busy to be there with you and offer support, pain relief options, meditation techniques, support for the husband (which he really needed as it was a 28 hour labour and it is physically and mentally exhausting for the husband as well), so they worked great as a team of two people giving each other "breaks" which in turn helped them be better for me.
She comes to your home a couple of times during your pregnancy to meet with you and your husband to help answer some questions about pregnancy and help prepare for the birth.
She is very knowledgeable about the different forms of pain relief medication but is not a doctor like a midwife and does not deliver the baby.
If anyone is looking for a fantastic doula who is very kind, warm and makes you feel really comfortable during the entire pregnancy and birth experience, I would highly recomend Joanne Raines - Whispering Heart Doula Services. www.torontodoula.ca