M.,
You may want to assess your baby's personality. They DO have personalities, even in the womb. The personality he has may influence your approach.
More suggestible kids with more easy going personalities are probably more susceptible to sleep "training." These kids just throw in the towel after a while and do it your way, much to the sleepy parent's delight. Some never put up a fight at all. They just go to sleep without much fanfare. Others fight initially, but then get tired of fighting you and simply learn to go along with your rules, even if they don't really like them. These kids may not be real "changemakers" in society, but they can be really good team players. They may not be leaders, but then again not everyone is born to be a leader. They like to get along. Conflict makes them queasy. Any old approach will probably work for these kids, as long as it is consistent enough to communicate your message to them.
However, kids who have stronger, more determined personalities don't give up easily (these are the changemakers, innovators, etc.). They may show more stubborness and not "fall for" your well intentioned sleep training tactics. They are simply not that stupid and not easily convinced that your way is best for them. After all, isn't it nicer for them to cuddle close and have you near? Why should they sacrifice that? These kids are tough negotiators. You're going to have to make a really good argument (without words of course) to these kids to convince them to agree to being shipped down the hall out of your hair. Even harsh cry it out doesn't usually work for these kids. They simply will not be deterred. They demand more than their easygoing counterparts. They may just get angrier at you, and resent your insensitivity. They may feel betrayal - when I cry, you don't come; when I need you, you don't have the time. They may learn to detach from you, which is not a good thing when you are a parent who wants to be involved in your kids' lives. They are more high maintenance, but the rewards of sticking by these kids can be great. The "No Cry Sleep Solution" by Elizabeth Pantley might be the way to go here.
Good luck!