A friend of mine changed the oil in his 86 Volvo 740 wagon every 1500 miles from the day he got it until he sold it 11 yrs later. I looked under the valve cover at 60K and all parts looked like they probably did at the factory-no varnish whatsoever. I change the oil in my JD 285 lawn tractor (18 hp liq cooled Kawasaki ) every 25 hrs and it too has zero varnish. Granted this may be excessive but I've seen the results obtained at the other end of the frequency spectrum. I do all of my car's changes at 3000 miles.

The CR story really made me think carefully when it came out but I ultimately reached the same conclusion as Larry B, clean oil will never hurt you. It's the cheapest insurance against wear/gunk buildup that there is. I buy whatever oil's on sale and use good filters.