The new polls in electoral race in USA.... Have they already started?

This morning I was reading the news:

New York Times: Here.
Washington Post: Here.

New polls in USA are always fun because it's amazing how they can ask something for 600, 700 people and after say that such result is a forecast of the official ballot results.

Two questions here:
1) The methodology used is questions through telephone calls or internet, using specific points. In this case, the gay marriage. Is possible to have a trustful answer through telephone based only in one maybe not so important point of the campaign?
2) Ok, ok, it's difficult to chance the republican primaries results but.... Is possible to ask to the people their vote preferences based on an unoffinal candidate, like Romney?

These things make me think...

OR, maybe a third one: 600, 700 people are enough to measure this kind of data?

Well, by now, all the polls already published you can access here.