I decided to save myself a drive today and stop by my local (small) dealer rather than drive down to Austin for my 10,000 mile service. I took Mobile1 with me for an oil change and the service manager came back around and said that two of his master-technicians at the same time told him that putting synthetic oil in my Prius would void the warranty. I had them pull it out immediately and drove back home. On the way home I called Champion Toyota in Austin and made arrangements to come see them... they offered to SELL me the Mobil-1 when I got there if I wanted. (I'll still take mine) What the heck is the deal with this warranty-voiding story?