Now, the baby obviously recognizes the familiar words and familiar voices, but that doesn't mean that the material read will have an impact on the baby so far as significant intelligence goes. This article from Penn State puts it well.
So is it worth doing? I put it in the category of "it doesn't hurt" and even "it is a good idea." Some people are strong advocates of it (see this blog for such people). I figure it at least gets baby familiar with your voice and can significantly strengthen your feelings toward your child.
All of my children have been read to while in utero. I read Brayden scriptures and stories while he was in the womb. Why not? Then of course my girls all got it because I was reading aloud to their siblings. There is no harm in it. I would also say there is likely no harm in not doing it, so if you didn't do it with your first, I wouldn't worry that you have somehow delayed his learning ability forever.
Here is something I think is worth your thoughts: If a baby can be born and recognize a paragraph that was read to her every day in utero for the last 1.5-2 months, "Imagine how much can be accomplished when a child can see and touch the book, understand the words, and feel the reader" (page 24). I think that thought is the where the real powerful implication of this study lies. If a developing baby can learn that much through your uterus and amniotic fluid--and only through hearing--what can a child learn in front of the actual book? Reading to our children is absolutely worth our time and effort.