It's amazingly accurate. I know because I spotted a discontinuity just north of Stedman, NC. I quickly recognized it as the long driveway into a Marathon convenience store, very popular with RUSA riders and local roadies. I've ridden this exact little detour countless times.
Here's a live map centered on the Stedman Marathon: http://labs.strava.com/heatmap/#15/-78.69499/35.05709/blue/bike Click the Google Street View icon to see from a rider's perspective. Then zoom way back to find your own locations.
Enjoy this amazing resource for route planning.
