I talked to a service mgr at a local Ford dealership about this just the other day. He said that the main advantage of the synthetic is that you can go longer between changes. He said that the blend, which all conventional oils are now, changed at 3K miles is just as good in his opinion. He said that the svc dept will do whatever the customer requests. If they want full synthetic then they do that. He said that they haven't seen any real differences in problems between using either one. Just my 2 cents. I'm too old school. Every 3K oil and filter for me!
I was told by my oil supplier that most of your major brands of "conventional" oils are actually blends. He said they may not say it on the label but they actually are. In our store we carry the major brands, and some of them are starting to change their labels and say synthetic blend instead of conventional. 
