It sure won't hurt your vehicle to change the oil every 50 miles if you want to. However, with the economy tightening and improvements in dino lubricant technology over the past couple of decades, quality non-parafin-based motor oils can easily exceed even 5,000 miles of service barring "rough service" conditions. Some high mileage fleets do oil changes at 5k-7.5k and filters every other oil change with no significant maintenance cost increases.
The general state of tune and condition of rotational and pressurized engine parts have more to do with the useful life of lubricants than anything else. The older and more wear, the less the useful life. Unless dino oil is thick when hot, black, and/or contains particulate, there's no way to tell if it's exceeded it's useful life. The real way to determine it is with professional analysis.
Most who subscribe to the 3.5k oil change ditty also think that if 87 is good, 90+ is better. Off roading? It's an altogether different ballgame.