You can use the bias calculation to estimate where things are headed. If you think turnout will boost your candidate by N points, add that. If you think that one candidate will gain X points at the expense of the other, add 2*X. For instance, if turnout will increase Kerry’s vote by 2 points, but Bush will pick up 1.5% of voters from Kerry, then the bias is 2 – (1.5 * 2) = -1%, or 1% to Bush.