Scheduled maintenance, when?

[Zing]

I once lived next door to this family of mechanics - dad + 2 sons. Owned a large service station, lots of experience, great mechanics, nice guys. They used to tell me that changing the oil frequently was the single most productive thing you could do for your car. They'd say 3,000 miles was the ideal interval. I've stuck to that and the cars I've owned had no real engine problems. If I'd ever brought my car to them they wouldn't charge me, so their advice was unbiased. So I always relay this advice to friends.

Tires are less critical, since the worse thing is wear on the tires, but I'd say every 6,000 or 9,000 miles is fine.

One thing I'm not clear on is transmission oil. I never changed it in previous cars, and my current mechanics says every 30,000 miles. I don't remember what my neighbors recommended.