where we agree then, i think, is the fact that Twitter's just another datapoint. and from a statistical perspective, it cannot be considered representative of the wider population for any number of reasons, not least the fact that it's observational rather than a random sample.
that said, it's an interesting proxy for examining questions of sentiment, and its predictive ability has been examined several times academically within specific contexts (elections and markets - e.g. this one by Cornell http://arxiv.org/abs/1010.3003) and found to be relatively accurate.
so agreed, it's not representative. but that doesn't mean it's not interesting and potentially useful.
that said, it's an interesting proxy for examining questions of sentiment, and its predictive ability has been examined several times academically within specific contexts (elections and markets - e.g. this one by Cornell http://arxiv.org/abs/1010.3003) and found to be relatively accurate.
so agreed, it's not representative. but that doesn't mean it's not interesting and potentially useful.