Hi C.,
No, we didn't let our baby cry it out. He's 2.5 and we still respond with warmth and empathy. Interestingly enough, he doesn't go on crying jags or throw temper tantrums to get his way...he doesn't see crying as a way to manipulate, probably because he knows that we will still be consistent about whatever we say no too while acknowledging that he's sad.
As a nanny I was asked to do CIO with babies whose families were "Ferberizing". It was heartbreakingly apparent that a 6 week old child screaming their little heads off didn't need isolation and deprivation, but to be held, soothed and loved.
Brain science now shows us the deleterious affects of the stress hormone, cortisol, on the brain. For children who are left alone to cry regularly, the cortisol can actually damage the brain. This is why our instinct as parents is to pick up our children. I'm not saying a little bit of CIO is going to cause loads of brain damage, but if you see the relationship between child neglect and learning disabilities, it's something to consider seriously. ("The Science of Parenting" by Margo Sunderland has more to offer on this.)
Lastly, it teaches a child to learn that their caregivers will not come when they need it. I don't want to teach my child that I am undependable, and Fend For Yourself isn't an age-appropriate message. Ferber was disgusted and saddened that this approach is the new norm: it was intended for *real* sleep problems, not to be a tool for self-focused parents to "correct" their baby's necessary wakings for food and comfort. Long answer, but there you have it.
It would be interesting to see a follow-up comment from you, C., as your own opinion. Even if we don't agree, I think it's an interesting question. Hope we can all be polite.;)