This is what the State of California says. Or more exactly what the California Integrated Waste Management Board (CIWMB) says. The fact is that most drivers (including myself) change their oil every 3,000 miles (or 5,000 km) even though many automakers now recommend service intervals of 5,000, 7,000 or even 10,000 miles for most modern cars.
Research by the CIWMB shows that nearly 3 out 4 Californians change their cars' oil before it is really needed. This generates millions of gallons of waste oil, a product which is potentially very polluting.
CIWMB has released a website that explains this "myth" and has a short list of recommended service intervals for common cars. For example, a 2007 Nissan Altima can have its oil changed every 3,750 miles (25 percent further than 3,000 miles), and a 2007 Chevy Malibu every 7,500 (150 percent more). The rule is that we all should check this figure in the owner's manual.
Please note that this figure also depends on your driving habits and the quality of the oil you're using. Changing oil too late is also a very bad practice, because not only you can damage your car engine, but it increases fuel consumption and reduces performance.
[Source: CIWMB (Thanks to my buddy Mike for the tip)]