I'm not sure where exactly to post this, but I figured here is as good as any place. YouGov conducted a poll a few days back that showed Obama leading Romney by 1 point (48-47). In the same poll, the hypothetical question was asked:
"If this year’s Presidential election were a contest between Democrat Hillary Clinton and Republican Mitt Romney, who would you vote for?"
Hillary Clinton: 51%
Mitt Romney: 45%
688 LV/1000 RV
MoE: 4.6
http://image.guardian.co.uk/sys-files/Guardian/documents/2012/11/02/ClintonvObamamk2.pdfI think this poll is somewhat insightful at least in showing how much of the SoS' non-partisan favorability would be lost if she runs.