Cool idea, but the results don't look right to me. I analyzed myself (@jasoncrawford) and its positivity scores for my tweets don't look strongly correlated with the scores I would give by hand. A tweet about “fucking terrible” customer support got an 88.7% positive rating. A tweet starting with “My favorite thing...” got only 39.6% positive.
Same. Love the idea, but tried a few obviously positive/negative people and got "completely neutral" for all.