That's a very good question. I should be able to see Everest from my roof, or Europe, or at the very least, the Atlantic Ocean. I might need a pair of binoculars or a telescope to be able to make out the first two, but I'm less than six hundred miles from the Atlantic Ocean, on top of a mountain in the heart of the Appalachian Mountain range, and all of the taller mountains are in the other direction. I should be able to see the Atlantic Ocean. I can't. Just the edge of the horizon. Kinda odd, isn't it?
Edit: wow, responses to the original post sure piled up fast in here...