Adoption can be a very difficult thing to deal with. Sometimes there are circumstances that are out of peoples control, or others it is just an immaturity level that leads to the decision. There are instances where it is definitely the best decision for both sides, others where the kids are in much better situations, but there are also times where there are some horrible results bouncing in between foster care and other bad situations which can lead to lives of crime and other unfortunate circumstances. Everyone has their own reasons and it cant ever be easy to come to that decision and give up a child. It is also very commendable for people who do adopt children as it is one of the greatest gifts that you can give that child to invite them into your home.
I know plenty of people who were adopted. Most of them went out and met their biological parents. It normally goes one of two ways. Either it goes poorly or it goes well.
I guess you could say that about most things but in this case it is particularly interesting. Either you realize you are better off without them, or you have a new, great relationship.
As far as I can tell, no one seems to regret meeting their bio-parents. Good or bad, that knowledge is something worth having.