I was so unbelievably anti-CIO, and I was SURE that LO would cry for hours on end. People would suggest letting him cry all the time, and I would get mad or defensive. I was 100% certain that if I let him cry, he would cry for hours. But LO wasn't sleeping well at ALL, and I didn't know what else to do. Some nights he would wake up every hour, all night long, and I thought I would lose my mind. I read "The No Cry Sleep Solution" with high hopes, but it honestly didn't help.
It wasn't until a month and a half ago, at 4:30am, after he had woken up four times, that I finally was desperate enough to try it. I had nursed him, rocked him, burped him, and put him down asleep, but as soon as his head would touch the bed, he would wake up and cry. Literally the second I'd start to pick him back up, he'd stop crying and go right back to sleep. So I was leaning halfway into his crib, making a loud "shushing" noise, patting his back with one hand and kind of cradling him with my other arm, and I suddenly realized that I really, really wasn't helping my son learn to sleep. I left his room, and he cried for 23 minutes (longest 23 minutes ever!), but then he slept for the rest of the night. The longest he ever cried was 30 minutes on the second night (I caved in and rocked him to sleep after 30 minutes, so I don't know how long he would've cried that time), but the next night he cried for 10 minutes, and the night after that, it was only four. I still put him to bed asleep, but if he would wake up during the night, I wouldn't go in.
It's a month and a half since the first night I let him cry, and now he is consistently sleeping 12-13 hours without crying or needing me. Like PP said, he still semi-wakes up/moves around at night, but he can just go back to sleep by himself now. The only reason I know he wakes up is because we have a video monitor and I sometimes see him do it. He'll sit up, move around a little, lay back down, and be sound asleep again without ever making a sound. I still nurse him to sleep for naps and bedtime, but once he's down, he doesn't need me to come back in. It's glorious.
I liked the book "Healthy Sleep Habits, Happy Child" (although admittedly I haven't read it all, since it's long, and I'm just enjoying being able to sleep now.) You might want to check it out. He has a lot of good things to say about how babies sleep and how to help them do it better. I don't agree with/do everything he says, but there are some helpful insights.