Have never done it. But seeing my spouse have no two pregnancies alike, and one of them almost ending in death, I think it's a pretty darn big risk to make for people you will have no real connection to. How would you feel if you were able to deliver for total strangers, but when you were ready to have more of your own, you can't because of unforseen complications. Can you live with that?
I also agree with the bonding concerns. I don't think genetics and biology are the only things that play a role with bonding...otherwise adoptions, and IVF would be a bust.
What if you're carrying multiples? Are you ready for any potential physical, psychological, emotional changes? Are you open to changing your lifestyle to accommodate the wishes and needs of total strangers? What if they insist on diet changes or something you wouldn't ordinarily do?
While you'd only be housing the baby(babies), how would you feel if you were raising a child for a couple who doesn't share your morals or values, or plan to raise the child in a way that you wouldn't agree with?
Hope you find more feedback from someone with experience. You might find articles online. I have read that there is a higher incidence of depression and other issues for surrogate mothers after delivery. Separation issues. Others saying compensation isn't enough for the amount of work etc. involved.
http://ezinearticles.com/?The-Third-Party--Surrogacy-and-...