Strava

It's really not that bad (as covered earlier in the thread). People just shouldn't expect anything even remotely accurate if they're using damn iphone/strava apps where the plotted course of a ride is wildly flying all over the place all the time.

If you're travelling at a fairly constant speed and you have your weight and your bikes weight put in correctly, AND use a decent GPS device you should be able to be fairly confident of a reliable estimate

You've never ridden with a power meter have you?