According to the research of Robin Dunbar, Oxford Professor of Evolutionary Psychology, the human brain can only sustain 150 social relationships at any given time. Of these 150, only 5 or so are your closest friends, somewhere around 20 may maintain regular contact, and 50 is right around the outer boundaries of your personal network.
The idea behind Path is based on this 50 person limit, something that Path hopes will let you communicate, via mobile picture, what you are really doing rather than throwing a filtered stream of data onto Facebook. Path is calling itself a "Personal Network;" not really competing with social networking platforms but augmenting the way that you show what you are doing. All you do in Path is take a picture, tag who is in it, where you are, and what you are doing, and then share with the people that you choose. There are no friend requests or following buttons, just an option to share with the 50 people that you are closest to. The resulting image/time stream (which is extremely slick) shows the "path" that you have been taking in life, letting actions supersede words.
The success of Path will really come down to whether or not people will want to buy into another social network/location platform. For all of its great abilities, it lacks much of the depth that other platforms have that make them successful. For instance, it's a great way to share where you are with your friends, but if you want to post a photo album, like you can in Facebook, you're out of luck. As a quick photo sharing platform, it's much nicer than Twitter, but lacks the ability to write in customizable blurbs. As a location service, it's more personal than Foursquare and that group of apps, but it lacks awards, Twitter/Facebook integration, and coupons that make those services thrive.
One thing is for sure... if Path doesn't thrive, it's certainly not because of its lack of style. The Path app is by far the nicest social networking app that I've ever used on the iPhone. The feature-set is a bit utilitarian, but the slick expansion of photos and the fantastic map views put this one over the top.
Be sure to pick up this fantastic looking app today... it's free in the App Store and is just waiting to be populated with the photo tagging, location sharing, privacy concerned masses.