When Google Maps first appeared on the scene, it wasn't a big game-changer in the online-map market. Mapquest was pretty well-established, and Google didn't really seem to have much to offer that Mapquest didn't have, apart from the ability to click and drag the map around (hey, in 2005 that was a big deal). But over time, Google Maps has become less about just maps and has evolved into a visual interface for all kinds of information, a sort of two-dimensional version of Google Earth, the company's 3D satellite-imagery service -- especially with the ever-expanding "Streetview" feature, which shows actual photos of the location you're search for (not available in Canada yet).
It started small, with features such as the ability to integrate Google Maps and the GPS in your phone or BlackBerry -- a feature that has saved me from getting lost many times, and effectively turns your phone into the equivalent of one of those dashboard GPS units, at a fraction of the price. Then Google started allowing you to add "user-generated content," such as your own locations and custom maps (something which has helped the company map remote parts of countries like India). You can do things like clicking two points and Google will calculate the distance between them, or list historical monuments in a certain area.