Interesting article from the NY Times on the accuracy of primary polling and the dangers of using them too far away from the election itself:
the polls have been pretty awful at most points prior to about three days before the election, seeing surges and momentum shifts that often dissipated.
The chart below tracks the error in the polls and compares it to the number of days in advance of the election that they were conducted. The error is measured by looking at how much the polls missed the final margin between the top two candidates. For example, if Newt Gingrich beat Mitt Romney by 12 points in South Carolina, and the poll called for Mr. Gingrich to win by 5 points instead, that would count as a 7-point error. And if the poll had forcasted Mr. Romney to win the state by 5 points instead, it would represent a 17-point error.