ohh, I have a feeling this will kick off..
Before having DS I read Why Love Matter's by Sue Gerhardt and alot of it is about the stress response in babies and how a baby that learns that no one comes when it cries may be a risk of developing emotional problems.
As far as I know, controlled crying isn't the same as letting babies 'cry it out'. In CC the parent goes back and reassures the child then leaves again - the child isn't just abandoned. The book is especially concerned about this happening to young babies as the brain goes through very precise growth spurts in the first year or two of life that directly seem, on evidence, to have a profound effect on their emotional development.
In a much broader sense it may even point to the reason why there is a much greater prevalence of depression today which, has been steadily growing since the mechanised work system was developed and peoples lives became centred on their work and not their children.
But personally, apart from anything else, I couldn't leave my DS to cry it out. I get flooded with hormones when ever he cries and, yes, I can't stand it but that response is there for a reason - so you will go to them, not get them out of earshot.
The horrible extreme of letting babies 'cry it out' was the fact of the orphans in Romania who were never picked up or comforted. This is an extreme case, but it because of these poor children that alot is now known about infant neurology.