The Sienna has gotten about 20k miles a year for the past ten years or so. It's driven daily around our (small) town, and on trips of 500-750 miles every couple weeks, plus a few bigger trips a year (we usually do a summer trip of 4000 or so miles). It gets some synthetic 5w30 (it's been Mobil 1 usually, but I don't stress it) and, usually, a Toyota filter every 7-10k for the most part, but as low as 5k if it's the dead of winter and getting short tripped badly, if I have time. It's specced for 5k with dino 5w30 so I figure synthetic is good for about double that. My mom drives it so I try and keep on top of that sort of thing for her, as it's not on her mind.
The Camry gets 15-20k miles a year from me driving the 300 miles each to college and back, plus assorted road trips from there and when at home; it doesn't see much in the way of short trips, and they are always followed by long highway runs. I usually take care of that with a 0w20 synthetic (now, Mobil 1 EP) and Toyota filter at 9-10k.
The Silverado gets some bulk 0w20 from the local Chevy dealer usually at OLM 15 - 0%, which ends up being a bit under twice a year.
None of our vehicles have ever needed an ounce of makeup oil, but I do check just because (usually when cleaning the windshield etc. before a longer trip).
Good question; I've enjoyed reading the responses. All told, we drive right around 50k a year between the three of us. I think we buy in the neighborhood of 2250-2500 gallons of gas a year, as a point of reference. Yes, lots of driving.