Wading into the minefield
First up: a neat bit of research on fetal pain. There have been several different ways that fetal pain has been used by the anti-abortion crowd, whether by requiring doctors to anesthetize fetuses, requiring doctors to tell patients about fetal pain (despite lack of clear evidence that it exists), and I believe I've seen reference to requirements that school classes present fetal pain in the course of a sex ed class. The idea is that you make having an abortion seem scarier than it already is, and to privilege one set of views on the underlying question of the moral status of a semi-developed fetus.
The research, ably described by Dr. Myers, shows that a developing human cannot feel pain until well after birth, perhaps not until around the second birthday. Of course, this all depends what pain means. If it's just nervous responses, you see some sort of stimulus-response pretty quickly, though not so early that you couldn't justify the 90% of abortions which occur in the first 10 weeks. If you take the view that the paper's author expresses, that pain is something that human beings learn about as part of their mental development after birth, the anti-abortion argument can be turned into justification for infanticide.
Which view is right? I don't know, and I expect everyone would pick a different answer. Because the people who would pick simple neural responses, or even simple cellular responses to damage, are the people who say that life begins at (or near) conception. The people who take a more developmental view will be those who advocate for the recognition of the grey area between an unfertilized egg and an adult human being, and they'll want people to be able to make their own choices.
Another thing that people trot out in arguing against abortion is the mortality rate associated with it. For instance, the recent deaths of two women taking RU-486 has raised calls for it to be taken off the market.
But as Matt Yglesias points out, even at its newly increased mortality rate, abortion is still less dangerous to the mother than childbirth is. Again, the anti-abortion argument can easily be spun into a pro-abortion argument. Indeed, one could turn this one into a call to require abortions to save lives.
And that last point is one we should dwell on. If the government can regulate your childbearing decision by forbidding abortion, why couldn't the government also regulate that decision by requiring it? Roe v. Wade doesn't just protect us against forced childbirth, it also defends against forced abortion. If the latter is wrong, are we sure the former would be just?