I've been a doula for almost 2 years now. I'm "hiring" my best friend who is a doula to be with me at the birth. I would never birth without a doula. For one, my dh needs some severe instruction and help (found that out the first time around). Secondly, my doula will know exactly what I want and need to help me labor more effectively...she will make me feel safe enough to birth. There is something special about another woman- unattached from the responsibility of safety of the birth- helping me through.
Lots of people ask "You're a doula and know enough to get you through birth, so what's the point of hiring one?" And the answer is this: When I'm in labor, I will have the mind of a laboring woman, and not of a doula. I will be just as likely as other women to have the "transition breakdown", the scare of not being able to do it, being afraid to push, etc. My doula will function very much as emotional support to get me through those hard times.
Definitely investigate your doula options if it sounds like you'll be wanting a doula. It's never too early to check out your options.