Social Applications
Social applications (apps), primarily games, are the new force. I'm not sure of the business potential (e.g., monetization) but they are a force to be reckoned with. For example, Tap Zoo is my son's favorite game and wants "neighbors" so he can get new animals.
Blogs
Inside Social Games: Tracking Innovation at the Convergence of Games and Social Platforms
Articles
Freemium will fuel the enterprise
iOS social apps attracting more eyes than top TV shows
Social Virtual Goods Sales Overwhelm Advertising Revenues On iOS
Flaunt It: Social Apps for Broadcasting Your Brainpower
How Location Based Social Apps Are Changing Business
Freemium