Are we happy yet? Facebook's National Happiness Index tracks our mood

We probably don't need Facebook to tell us that Thanksgiving is one of the happiest days of the year, but that's among the conclusions found in the new Facebook Gross National Happiness index. And you probably wouldn't be shocked to see huge spikes in happiness on Mother's Day, the Fourth of July and Christmas.

Though unsurprising, the index's results confirm the principal reason we join social networking websites in the first place -- to meet and interact with friends and family. But the results also show how we are beginning to use sites like Facebook and Twitter as national gathering places during major events, including when major tragedies strike.