Even before he has been officially designated as President Obama's pick to be Fed chair, Summers is already slowing the economy and costing jobs according to the New York Times. This remarkable possibility is due to the fact that investors do not see Summers being as committed to maintaining an easy money policy as the current Chair Ben Bernanke or his main rival Janet Yellen. The result is that interest rates are higher now in expectation of future rises. This is of course speculative, but it is nonetheless an interesting hypothesis.
It is also worth noting that all the reports that President Obama has decided to pick Summers are based on anonymous sources. This is likely part of a campaign to push Summers' candidacy, since opponents will be less motivated to act against Summers if they believe the decision has already been made. As long as no one has gone on record identifying Summers as the pick there is zero cost to Obama making a different selection. Only the reporters would look foolish.