I went to using Mobil 1 in my 7400# F350 with V10 in hopes that I might just get a bit more in gas mileage. Nah, not a chance - it was 11mpg before and, guess what, 11mpg after. So instead of my oil changes costing $40+/- every 4-5K miles, its less then half that by using the Motorcraft semi synthetic 5W (or 10W)-30 (it takes 7 quarts) and I still get around 11mpg with 13/14 on long haul trips or 9/10 with my 12K camper hung on. Wear and tear - half a quart in 5K says there isn't much at 56K miles.

So with that said, there probably isn't much need for full synthetic oil. It might help starting below zero, but my truck sat outside last winter and started every day, including several -5 or more days. Is it good stuff - yep, but not that much better then a semi synthetic. What, IMHO, it boils down to - oil company advertising !! And yep, there will be some here that swear by it as well.