Personally don't think either of the Williams will make the finals; but they do get motivated for the Grand Slams. While both women are very talented, tennis doesn't seem to be enough of a focus, and age is beginning to be a factor for them.
On the men's side, Roddick seems to be really struggling. I think Djokovich, Nadal and Federer have the most potential as finalists. But we still have almost a month before the Open, so who's going to stay healthy?