In the world of raising children, there are many parts that make up good child rearing. Trying to take one issue and say it does or does not produce "fine" children (though we should be talking about godly children, but that is another story!) is inappropriate.
Some could say they allowed their children to watch R rated movies and they "ended up just fine." Others could say they provided condoms to their child and they "ended up just fine." So the issue is not "ending up just fine" but what does God desire and want in the lives of our children?
Quite honestly, I dislike these discussions because individuals start in an "argumentative" mood - desiring to "win", not to "understand" the mind of God. We are so fast to want to assume we have the mind of God and can understand things because of our experience or our mental awareness, rather than through an immersion into the Word of God.
Quite honestly, after 20 plus years of working with children, I would say 75% of all children, perhaps 90% of all girls would do just fine without spanking. Obviously our world is full of people who are not disciplining out of love or out of self sacrifice and servant hood to their children. We could point them out as great examples of those who did or those who did not "spank" using their results of parenting as an example pro or con!
What disturbs me most about such discussions is a sense that we solve problems or come to conclusions without an understanding of God and His revealed Word.
I have written a short booklet on discipline which you can download at:
http://llbook.colossians2.com/
I think it mentions spanking in two sentences!
Most important is that you love your children! Love them enough to set limits according to God's Word. Love them enough to disciple them! Love them enough to punish them (as God's Word clearly states - the father who loves his child will punish them) when they do wrong! Love them enough to teach and train them. (Duet 6) Love them enough to hold them accountable!