Happy Birthday, Twitter!  The social networking site is celebrating its fifth anniversary.  It’s hard to look back in a pre-microblogging world, especially when you take into account the impact it has had on many historic (Iranian elections), political (2008 Presidential race) and lifestyle events (World Cup).  Further, we cannot forget that nearly 140 million tweets are sent daily.

March Madness or Marketing Madness?  As millions of Americans tune into college basketball games this month, companies are seizing the moment as one of the biggest marketing opportunities of the year. Coke, for instance, is in the midst of a social media promotion that includes an online gathering place with tweets about the games, dubbed the Coke Zero Social Arena. As the “official pizza” of the NCAA Tournament, Domino’s is hosting a bracket contest on its Facebook page. Did you complete a NCAA Bracket? If so, how are your teams doing?

One of the biggest challenges to marketing departments is determining the ROI for social media campaigns. Although it is of course different for every company and campaign, event registration site Eventbrite would tell you to put your resources in Facebook. The site found that a Facebook “like” drove more sales that a Twitter post, and consumers shared events on Facebook nearly four times as often as they did on Twitter. Interesting!

The New York Times announced it will limit free digital content. Under its new paywall, readers will gain access to 20 articles a month for free. There is a loophole, though, as the news source – for now – will not limit access to article links from Facebook or Twitter.

Check-in lines at airport counters are so last year. Through its Ticket Counter Facebook application, Delta travelers can now check in to flights and print boarding passes.

Where are you going? An interesting study on GPS use was released last week which, based on data from 20 million subscribers, determined that Wal-Mart is the top destination search — followed by Target and Starbucks– and Washington, DC residents used the devices most frequently.