Seems to me that online maps should render the Earth as a sphere (or, heck, a properly shaped spheroid) centered on the viewport, where scrolling around rotates the sphere. This will look flat when zoomed in, will look accurate when zoomed out, and won't have any weird distortions of area or direction. I'm sure Google Maps didn't do it this way originally because it wasn't feasible when your minimum target was IE5 running on Windows 98, or whatever, but it surely could be done now.