finally had to throw my .02 cents in.
I had a Mazda MPV with 4 cylinder for years and always changed the oil at 3k miles (Castrol 20-50W). At 125k the wife ran it after the radiator came apart and I had to rebuild the engine. The internals were absolutely spotless and you could still see the cross hatch on the cyl. walls, along with the scars from running hot. Now I change oil between 3 to 5k (still using Castrol 20-50W) and will continue to do so until something indicates that I should do different. The secret to running these things for many miles is like Larry says - change it hot and change it often.
'97 Honda CRV