Ford has published a chart for the dealers with their latest recommendations on oil viscosity. It is true that they recommend 5/20 on all Duratec engines. If you have had your oil changed recently in a Ford dealership it is very likely that they used 5/20. There are not very many engines in the Ford product line built in the last 10 years that are not on the 5/20 list (a noticable exception is the Focus SVT).
Although I am not aware of any problems from using the new oil, I'm also a little gun shy. I still use 5/30 in mine.
For what it is worth, the Motorcraft 5/20 is a synthetic blend (semi synthetic?) while the Motorcraft 5/30 is not.
