Is Twitter Making Us Depressed? Study Of Tweets Reveals 63M Users 'Are Becoming More Unhappy'

For millions of users, Twitter has become the place to communicate every thought that pops into their head - and it turns out they are not very happy ones.
A study has analysed the 'happiness level' of more than 46 billion words written by 63 million people on Twitter around the world.
It appeared good moods were on the decline, according to researchers at the University of Vermont.

Tweets were interpreted using a service called Mechanical Turk. On this site, volunteers rated the 10,000 most common words used in the English language on a scale of one to nine for how 'happy' they considered them.
'Laughter' scored 8.5, for example, while 'terrorist' got 1.3.
Because each Tweet is timed and dated, it revealed shifting patterns in the way people were feeling.
The study found we have become less happy over the last few years and were most unhappy in the first half of 2011. However the Twitter study is far from conclusive of the general population.
Could this be true?