Ford Repair: serpentine belt on ford durtec 3.0, serpentine belt, quality belts

Question
I have a 02 Escape with a Durtec 3.0. No problems with it, but I am wondering when the serpentine belt should be replaced?

Answer
Every 30k miles is a good rule of thumb. However, it never hurts to go ahead and buy one. You can stick it in the trunk, or under the driver's seat as a fail safe. Your higher quality belts actually have diagrams on them, making them much easier to install.<Correction, I meant hatch, not trunk. It's a force of habit.>