As a mum who has lived through 3 frequent night wakers (and survived), there have been many times when exhaustion has left me wondering what I can possibly do to get some more sleep.  Many mums suggested leaving baby to cry it out. However, leaving my baby to cry is something that goes against my every instinct as a mother, I've always wanted to deal with my children's needs quickly and responsively and have always felt that if my baby is crying its because they need something.  This  article by the Analytical Armadillo gives some great insight into CIO and why it may not be the best choice for baby:

http://www.analyticalarmadillo.co.uk/2011/01/cry-it-out-potential-dangers-of-leaving.html