I put roughly 28,000 miles on my 2000 Nissan Frontier Crew Cab every year. I drive a little over 40 miles one way to work every day, plus weekends and road trips, etc. Since I bought my '76 GMC back in November, that may have dropped a little because I drive it when I can. It had approximately 136,000 miles on it when I got it, and I just rolled it over 140,000 this weekend.
Couldn't believe it either...I checked the gas mileage on a 160 mile round trip this weekend going fishing in the '76 and got almost 15 MPG.

That's running at around 60-65 mph the whole trip with the very tired original 350/th350/4bbl Q-jet. My Nissan only gets 16.5-17 mpg.
Mike