Social media moves so fast, it's hard to keep up. Here are the week's top stories in scan-friendly format:

  • President Obama Joins Foursquare
  • Google Plus Now Used By Mainstream Population
  • MI5 Searching Online For Riot Organizers
  • LinkedIn Prioritizes Mobile With App Refresh

President Obama Joins Foursquare

US President Barack Obama is no stranger to social media. The president gained a huge base of support during his election campaign due to the social networking efforts of Obama himself and his staff. He's already on sites such as Twitter, Facebook and LinkedIn. If you're tracking Obama's social media empire, add Foursquare to the list.

The commander-in-chief joined the location-based service and will be using it to highlight places he visits along with his activities there. This is a huge shot in the arm for Foursquare, as it will raise the service's profile. Obama jumped on the service just in time for his current road trip schedule through the Midwest, where he checked in to Cannon Falls, Minn., and a riverside park there.

To follow Obama on Foursquare, head to Do you think it's cool that Obama is on Foursquare? Does it make you more likely to join or further use the service?

Google Plus Now Used by Mainstream Population

About a month and a half after its launch, the demographic of who's using Google Plus has changed. At first, early adopter techy types were exclusively using the service; now the main crowd has skewed to suburban parents and well-off empty nesters. This is according to web traffic monitoring Experian Hitwise, which posted new numbers earlier this week.

At launch, Plus users were mainly in the "Colleges and Cafe's" demographic, which consists of early adopter folks who jump on new technologies easily, followed by "Status Seeking Singles." Fast-forward six weeks and now a large group using the service are called "Kids and Cabernet," indicating more prosperous middle-aged married couples in suburbs and financially comfortable empty nesters.

Are you seeing your Plus stream showing more topics that would indicate parents are on the service? In my experience, yes, this skew is definitely showing. How about you?

MI5 Searching Online for Riot Organizers

In the wake of last week's London riots, police and other agencies in the U.K. are seeking to find out who organized riots and other activities. The riots were said to be fueled by Twitter and even the private mobile messenger BlackBerry Messenger. Now the security service MI5 and the electronic interception center GCHQ are searching for people who organized last week's riots, according to the Guardian.

Trolling BBM will be hard for the service, as BBM has a security system that is hard to work with for police agencies trying to parse messages for criminal activity. However, GCHQ's networks and system can intercept pictures and audio files, then track the owner and work with mobile companies to try to narrow down the senders of such messages.

Using BBM rather than Twitter was key in the riot organizers' strategy, as Twitter is much too public to stay anonymous. By exchanging PINs, BBM participants can exchange messages in a one-to-one or group fashion. BBM messaging is much like text messaging -- just private and exclusive to the BlackBerry smartphone line.

LinkedIn Prioritizes Mobile With App Refresh

LinkedIn, the professional-focused social network, has reiterated its commitment to mobile with a huge refresh to its mobile application suite. The new apps for iPhone and Android are faster to use, simpler and emphasize Groups, a major feature of LinkedIn that is growing in popularity.

The new applications have simplified by focusing on four key areas: Updates, Inbox, You and Groups. The Updates section feature your newsfeed of activity from your network and lets you check out LinkedIn Today, the company's news portal. Inbox has all your messages and LinkedIn requests and the You section lets you gain access to and update your profile, view your connections and share updates out to your friends and colleagues.

Groups are emphasized in the new applications and makes it possible to gain access to the various Groups you interact with and browse discussion items, as well as post new items to the Groups. The apps are a welcome update and are much faster, especially on Android, and more useful too. If you're a smartphone-toting LinkedIn user, check out the new apps today.