Holly,
We did and do CIO with my 15month old son-and will with Michael too. He is almost 7 weeks old now so we're really just now starting it with him. (I just don't have the heart to do it when they're younger than this)
We do CIO at nap/bed time basically, when we know he's fed, burped and changed. He is usually okay if we lay him down with his pacifier, but if it falls out of his mouth-get ready for the screaming! lol
Our 15mo old does really well with it too. He is usually asleep within minutes of being put in his crib at night. We also put him in his crib if he is being naughty (we went through a short biting phase). We let him CIO then take him back out, if he doesn't fall asleep.
HTH
Roxi
Mom to Nicolas born 11/11/06
Baby Michael Jay is here! Arrived 1/11/08