Off the bat, I would say:
Skills will have to be retuned slightly, but not much. Most of the trappings will carry over, but some of them assume technology or contemporary cultures. Guns, obviously, has to go, to be replaced with Bows or something like that.
Buying and/or making things will be impacted, so the GM will have to rework the Buying Things chart, or just wing it.
Magical hexing should be replaced with a mechanism that conforms to Dresden's assertions that in ancient times, mortal magic spoiled milk and things like that: basically, have it do things which are inconvenient and easy-to-notice in a medieval setting.
Other than that, a lot of it will easily carry over.