Opal-- that's kind of what I was trying to say and couldn't find the right words yesterday.
I think that if you're a person with really good self esteem, really good boundaries and a good judge of character who also has a strong sense of self (i.e. you know your boundaries and have no problems sticking to them), then this article is a bit of a "duh, no kidding."
If you're somebody who is a good judge of character and knows what they think their boundaries should be but has had trouble sticking to them, or has been raised in an atmosphere where setting boundaries (i.e. not letting the other manipulative people do what they want) was frowned upon and emotionally beaten or guilt tripped out of you, then this article can be a reassurance that you are not a bad person for setting boundaries and keeping people who are not healthy out of your life. I say "bad person" because people WILL try to make you feel bad for not playing along.
And if you have no good boundaries and have a habit of picking people that are bad for you-- then this article can be a good starting point to learn what inappropriate and unhealthy behaviors are and start to see how to choose better, and what to look for in other people's behavior (both good and not so good).
Not all of us are at the same level, and so I can see why this article is alternately interesing and boring depending on where you're coming from.