1. Facebook - Five mobile social networks you need to follow

Facebook: The standard by which all other mobile social networks are judged. The numbers speak for themselves: Facebook users worldwide are closing in on the 500 million mark, up from 200 million users just 15 months ago, with about 30 percent accessing the service via mobile device each month. That percentage grows substantially within the smartphone segment: In June 2010, research firm The Nielsen Company said 39 percent of all smartphone owners use the Facebook social networking application every month, adding it is the most popular app on iPhone (used by 58 percent of consumers) and BlackBerry (39 percent), as well as the second most popular on Android (51 percent).

But to retain its sizable advantage over the competition, Facebook must continue to innovate and expand. With location-based mobile social networks like Foursquare, Gowalla and Loopt growing by leaps and bounds, look for Facebook to introduce its own geo-social services in the near future--rumors abound, with multiple reports indicating the company will soon integrate location tagging into users' status updates. Another possible clue to its plans: Earlier this month, Facebook acquired social travel startup Nextstop, which enables users to create and share vacation guides and tourist recommendations.   

With feature phones still making up the vast majority of the international wireless market, Facebook is also expanding beyond smartphones with the May introduction of 0.facebook.com, a new mobile site optimized for a speedier, more efficient user experience across mass-market devices. Targeted for consumers in developing nations, 0.facebook.com retains vital social networking features and eliminates components that complicate and slow down the process--users can still update their status, view their News Feed, comment on posts and send and reply to messages, but should they choose to view photos, data fees will apply.

Facebook's biggest threat? Facebook itself. Any change to the service inevitably triggers backlash from a small but vocal minority of users. Mounting concerns over its approach to privacy controls even prompted a grass-roots protest calling for members to abandon ship, but May 31's Quit Facebook Day turned out to be a bust--only about 31,000 users pledged to delete their accounts. Even so, Facebook introduced new, simplified controls promising to help users better understand what kind of information they're choosing to share. The site has weathered other controversies along the way, and still it continues to grow. For now, Facebook remains too powerful, too entrenched--and for most users, too addictive--to simply fade away.