I fall somewhere in the middle, using dealers for major services and a local mechanic for minor 5K services.
My reasoning (however flawed) is that if I were to buy a car with, say, 70K miles on it, I would be far more comfortable knowing it was dealer serviced at the crucial 30K and 60K marks and all necessary work was done (diffs, tranny, lubing, etc).
Basic oil changes and brake services anyone can do and I wouldn't care so much, as long as they were done. In those cases, why pay a dealer premium? And always keep all receipts and records of what was done.