There's so much of the world to see, and sometimes it just doesn't all fit onto a map at once. Previously, people have written custom Mapplets or Maps API pages to visualize their dense geographic databases, and that's still what we'd recommend if you are a web developer and want the full interactivity of JavaScript. If you don't need that functionality, however, Google Maps now offers a better view of KML files of similar density and richness, especially when they contain <NetworkLink>s whose servers' results are tailored to the part of the world that is in view. For example:

If you like these examples, try the 'Save to My Maps' link, just under the 'My Maps' tab, to keep them around so you can do things like view Panoramio photos while searching for hotels near a potential holiday destination.