Awhile back I was considering CIO when LO went through a rough patch, but decided it just wasn't for me (I can barely stand to hear her cry for 2 minutes let alone more than that!) and her sleep naturally improved on its own, although I am sure we will have more rough nights and regressions in the future but I am fine with that. We let her "fuss" a bit but I go to her immediately when she starts to cry. It works fine for us and I don't judge those who do it differently!

I recently came across this article on sleep training and some of the information in it made me glad we didn't let her CIO, but also made me wonder how true it is?? http://www.isisonline.org.uk/how_babies_sleep/sleep_training/considerations/

Especially this part:
A recent study demonstrated that mothers and babies undergoing a controlled-crying intervention started out with matching, synchronous, hormonal stress responses (babies cried at bed-time, their stress hormone levels increased, and their mothers' stress hormone levels also increased). After three days, babies had ceased to cry at night, and mothers' stress hormone levels dropped, however babies levels - despite the fact they were no longer crying - remained high. This suggests that the babies behaviour had adapted to being alone for sleep, but that their physiology had not. The response of the babies in this study lends support to the theory that babies who undergo sleep training via extinction may be learning to 'give up' rather than to 'settle' -- outwardly the two behaviours appear the same, but inwardly the babies physiology is very different. As well as being physically separated from their mothers, the sleep trained babies were no longer in physical synchrony with their mothers as their mutual stress response link (maintained by infant crying) had been broken.