In my opinion, saving money on engine oil changes is kind of like saving money by eating at McDonald's instead of Whole Foods. The immediate solution is saving money. The long term results may not be so great.

The oil discussion inevitably attracts anyone from the guy who uses drain oil in his oil-eating 1970s diesel farm tractor, to the fanatics who analyze their oil every 2000 miles, to determine if they can stretch a crankcase full of oil a little farther.

Neither discussion is particularly relevant to me, because they don't apply to my cars. The interval-stretchers don't drive my cars, under my conditions, in my climates, and aren't analyzing my oil. Since I don't send my oil out for analysis, I probably drain good oil every 3-5k miles, depending on conditions. I'm much less concerned about draining still-good oil, than leaving garbage in the crankcase. In my opinion, it's hard to apply someone else's scientific proof, to your unique driving habits and conditions.

Flawless engines like the Toyota 1MZ-FE have fallen victim to people who stretched the oil change interval. An engine that can run 200k miles with nothing other than oil changes (often not even a timing belt), was regularly ruined before 100k because of oil breakdown and deposits. This is only one example; there are others. I pick the Toyota engine because when driven with good quality motor oil that is changed often, the engine has no faults, period. The Volkswagen/Audi 1.8T, Chrysler 2.7L, and other engines have had similar problems.