There's that old electability argument again. How could those polls mean anything when the majority of those polled only know anything about those candidates who have received heavy media coverage for years. Whoever the Republican nominee is, he will receive enough media coverage to change any perceptions or non perceptions that are registered by these early polls. Also, see my earlier post on "electability".
Polls measure who people plan to vote for at the time the poll is taken. Whether they know what they are doing or not is beside the point.
Come November large numbers of voters will know rather little about the candidates. A substantial percentage will vote on the basis of how the candidates make them feel. Polls taken before election day will still be meaningful despite this ignorance.