I know this is likely to start a flame war but I found this interesting.
Here is a quote I found on another forum that makes a lot of sense:
Everyone is servicing as they were when we had leaded gas, Few additives in the oil or gas, blow by in engines even when new was enormous, filtering was at 100 microns. Design has come a long way since then and the simple fact is a lot of oil is wasted in the US by servicing today's cars as if they were in the 50's.
I found this related story on Yahoo! news:
http://biz.yahoo.com/ap/070321/autos_oil.html?.v=2
Synopsis:
Most major automakers agree: The adage that you should change your car's oil every 3,000 miles is outdated, and even 5,000 miles may be too often.
Anyone agree/disagree? Why?