I switched from standard to synthetic (Mobil 1) in my Lumina Euro with 90K miles on it. What I noticed right away was the engine seemed to start easier and quicker, probably less friction at start up. I think it had a bit better throttle response, too. It did leak a bit more. I've heard of this happening, not sure if it's true or a myth. Knowing that I was going to sell this car soon, and not wanting to spend the money for another syn. oil fill, I switched back to natural oil the next time. No problems that I know of. That fellow that had problems with his Ram, probably would have had probs anyway.
I haven't switched the Trep over yet, not sure if I will or not. I think for normal, everyday driving where I live (pretty cool climate) that synthetic isn't really necessary. If I drove hard, in a warmer area, with lots of hills, I would probably consider it more. I also like to change my oil often, and with syn. that gets real expensive, real quick!