Yeah, the difficulty curve goes up exponentially as you go out. If you can print at 100, then a decent drop chart can get you on target at 400. By 500-600, you have to be able to read wind pretty well, and being above or below your target will change your hold noticably. When you get out to 800 or so, wind can really screw you up, and you need to know your range within 10-15 yards. Past 800, depending on your chosen round, spin drift, density altitude, and other factors start getting noticeable.
One thing I've found interesting, is if you get a spotting scope set up, focused right, and near to the bore axis of the shooter, you can watch the trace of the round on flight. It's kinda mind blowing the first time you see a .308 apex out 15-20 feet over the target and arc in to it...