For my 99 Honda Civic, I do a 10,000 mile oil change with 5W-30 Mobil 1 Synthetic. At 5,000 Miles I only do a Filter change and add .25 to .3 quarts that were removed with the filter. I have a engineering friend that runs Amsoil in his Mazda 3 speed and changes the oil every 30,000 miles based on the oil analysis.
It takes synthetic oil, but Mazda insists that Canadian owners change the oil every four months or 8,000 km to maintain the warranty. I don't drive a lot, and the car doesn't have a monitoring system.