I don't think it will winnow the field at all, though it may give some candidates a convenient excuse to thank their volunteers and go home to do something productive.
Romney will win the poll; depending on who finishes second and third, there will be other stories to concoct. I personally hope all participants have a good time, and it would be good for the Iowa GOP to raise lots and lots of cash. Win or lose, it won't matter. The political media of the mainstream variety will waste trees and air injecting whatever meaning into all this, but we'd all be better off if they would let the campaigns do that; we'll expect the spin, and it will reflect the politics of the poll.
Read the whole story at the link above.