When I bought my Savage, I initially thought, "Big Single needs Premium" like everyone else, and I ran premium for almost 2 years. I thought that it couldn't hurt anyway.
In the winter of '02, I tore down my engine to fix the plug leak, and while there I decided to paint the engine. That meant the head and cylinder were coming off....And I got to see the piston.
I had a crappy digital camera back then, but here is what I found. (BTW-I edited this shot for Be_Savage)
Yesterday, after 5 years and another 12K miles of using regular gas, I pulled the head again.
Here you have it. 6 times the mileage as in the first picture.
Not being a chemist, I can't tell you the scientific stuff, but the general understanding is that premium burns slower than regular to prevent knock or ping. However, if the engine doesn't need premium it may not burn as cleanly either.
So, I will say it one more time. If you want to run premium even though you don't hear any knock or pinging, or because it simply makes you feel good. Go right ahead. It's your dollar.
PS - if you right click and "view image", you'll get a bigger picture.