Yes, Ford changed it in a lot of their cars a couple years back (including my dad's 01 Cobra) to increase their fuel economy rating. They say to put 5W-20 in a lot of their newer engines to balance out the terrible gas mileage their bigger truck engines get.
But to answer your question, I used Motorcraft 5W-20 up until 20,000 miles. After 20K I switched to Mobil 1 5W-30. I've gotten better gas mileage (not much but hey it's some) and noticed a little better of an idle when sitting at stop lights. It's definately worth the extra money.