I think it's best to look into this a little bit more. There has been some research that the CIO method is harmful in a LOT of ways. Physical, emotional, psychological etc..
I personally have never believed in the CIO method. I was raised by a wonderful family of women in a school of thought that it's impossible to spoil babies. If they are crying then they need you. It would be cruel and inhumane to refuse them that comfort. They are too young to understand anything except that you're not there when they need you.
They will not go away to college still needing to be rocked to sleep. Enjoy them while they are babies and hold them as much as they need. There are studies that support this and point to the idea that a baby that gets answered when they cry (i.e. picked up and soothed) actually turns out to be more emotionally balanced and independent as they get older. It's only in western cultures that moms don't respond to their crying babies. Babies are not adults, they do not need to "toughen up" or "self soothe". If that were the case then why don't we kick our kids out to fend for themselves when they're 5? After all, they should be able to feed, clothe and shelter themselves, right? Wrong! Children need adults for guidance, care and comfort. Asking a baby to "grow up" emotionally is unrealistic and I feel it's abusive. I'm sure plenty of moms will give me guff about that statement but this is the school of thought I have adopted as a parent and it works very well for me. My kids are very well adjusted and are not needy or dependent beyond the norms for their age groups.
As I've said a million times, you have to help them build their foundation if you want them to stand on it someday. They don't know how to build it themselves. Letting them cry it out is only going to let them know that mom isn't going to be there when they need her.
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Edit: Wow, Tarah J.! I thought we were on here to offer advice and opinions when they are asked, not to run down other moms' advice and opinions. You'll notice that I speak of my OWN feelings and conclusions and what has worked for ME. Maybe you should think about keeping the snarky comments to yourself. Or maybe it's just your personality type that can ignore a crying baby.