I've been questioning the value of polls here, so here's some evidence of how well they work. I was interested in Ekos Politics' claim that methods of predicting the seats won by each party in Canadian federal elections "work pretty well" (the quotation is from a PDF I can no longer find on their website, but I have a copy if you want one). Here are Ekos' final projections for the election of May 2, 2011 (you can verify them here):
Conservatives: 130 to 146 seats
New Democrats: 103 to 123
Liberals: 36 to 46,
Bloc Québécois: 10 to 20
Green: 1.
And the results:
Conservatives 167 seats
New Democrats 102
Liberals 34,
Bloc Québécois: 4
Green 1.
In other words, Ekos got the Green seats right and no other party's. Of course, there is no reason they should get them right. The regional variation in voting is so great in Canada (the BQ only runs in Quebec, for example) that you'd need extensive polling in each riding to even hope to approximate the results. Even then the non-representative samples you'd be working with would seriously limit the accuracy of your estimates.
At any rate, the Ekos projections missed the two important events of May 2: the Conservative majority and the collapse of the Bloc. Journalists will probably go on acting as if polls mean something, but that doesn't mean you have to.
