I USE to change my oil every 3K no matter what. It wasn't until I added AMSOIL to my business product offerings that I began to utilize used oil analysis to determine when I change it. Since I began paying attention to my results and the results of others, I noticed a nice trend. Whether it is AMSOIL, Champion, Royal Purple or others; there are quite a few technically superior engine oils out there today that can go much longer than expected in most cases.
I found that the key things to remember are, if you are not going to utilize used oil analysis, change your oil often and you will have a happy engine. There ARE advantages to extending intervals, but it isn't for everyone. But, changing the fluids more often than most OEM owner's manuals say is VITAL in some cases. Most user manuals do not account for changing power steering fluid, brake fluid, gear lube and the like often at all and this is detrimental to the life of hard parts. Your fluids are the life blood of your vehicle. Maintain them properly and the vehicle cost of ownership will actually wind up being less than if you ignore them.