I've bought Napa parts in the past with mixed results. I have ok luck with their brake parts but I had a premium hub/wheel bearing fail in 3 months on my grand prix.
I buy plenty of parts store stuff but there is a time and place for it. Some things are just worth the money for a better quality part.
Napa's premium stuff can be good, but alot of times you pay a significant premium for getting that part right away. We get gouged here in Canada. If I can wait 2 weeks for a part from RockAuto, I can almost always get a premium part online for less than what Napa would charge for an economy part.