Even if the manual says you can wait until 10K to change the oil, or the oil life monitor says you have 10% or whatever left with 5,000 miles on the oil, understand that by following these, you are doing the bare minimum. Kind of like waiting until you're on fumes before filling the tank, or showing up for work with 5 seconds left before you're late every day. You may be able to get by, but you're not doing yourself any favors.
If you want your engine to last, and never let you down, change the oil every 5,000 miles at the most, with a good quality oil of the recommended viscosity. You can probably go a little longer if you don't live in a cold climate and drive a lot of highway miles, but oil changes are cheap, while engines, downtime, and the associated stress in life are not. What is it going to cost you, maybe $40 more in the course of a year by being a little more attentive? If you can't afford this, you shouldn't have bought a new car. I personally like synthetic oil, and won't use conventional oil any more, but if your manual says you don't need it, you don't need it. Treat the car like you would a friend. You can get away with abusing the friendship or the car a little if you have some good karma from past deeds or using good oil and keeping up on maintenance.