He says that based on research (what research, it doesn't say), a person cannot truly be connected with more than 50 friends all at once, and interact meaningfully with 150 people on a social network. What happens, let's say in the obvious example Facebook, is some sort of a vain self-broadcast or self-promotion that doesn't really matter to most people. In fact, you probably don't know most of the people in your network.
That's why he created PATH. PATH is an app-based social network and photo sharing site which allows you to connect with only 50 people or less, and interact with people who really matter to you. This is where you can really talk about a problem at work, or a desperate situation you are having at home. You can post anything knowing that you won't be stalked by an unknown person, or be self-conscious. With PATH, you will know that whatever comment or post a contact makes, it will matter.
I have a pretty strong feeling that this won't turn into a behemoth like Facebook, since people and businesses thrive on anonymous people - and PATH is a Facebook app. There are already hundreds of thousands of users on PATH, but nowhere near the size of Facebook. But there will be some people who would create an account, and choose 50 friends who really matter.
I noticed that it asks for your entire profile information from Facebook.
I'm trying it out. Maybe you should give it a whirl, and take a break from the anonymity and bombardment of meaningless posts.