The 3D pictures are impressive, though they are so far available almost exclusively in larger cities; even there, get out into the burbs and you start to see only flat, squashed buildings. The images also render fairly slowly, at least in my experiences on the latest-generation iPad or iPhone 4S. One of my favorite hidden little features: Zoom out far enough in the satellite view and you'll eventually end up with a globe of the Earth you can spin around.
The 3D imagery also shows up in the traditional maps, too, with sketched wireframes of the buildings, which is also pretty cool--especially when you watch them rise out of the ground like stepping stones. (In some places, though, I found the wireframe buildings occasionally to be less-than-accurate in shape.) In 2D mode, you'll actually see the outlines of buildings shaded on the maps. They're surprisingly good--I could identify my house just by the outline.
Even better, you'll get little icons that identify businesses, eating establishments, schools and other points of interest. Tapping on these brings up an address, contact information, and even Yelp reviews and photos where available; for more info, you can jump out to the Yelp app, if you've got it installed. Google Maps on the Web has offered a features like this for some time, but they never made their way to the iOS app. While this might be old hat to those who already use the Yelp app, there are likely plenty of converts still to be made by virtue of the built-in nature.
When it comes to the maps themselves, it's hard to overstate just how beautiful and responsive they are. Apple uses a vector-based system for drawing the images rather than Google's bitmaps and, on the latest hardware at least, they practically fly. Zooming, panning, rotating, are all virtually instantaneous. Street names appear and disappear at appropriate levels of zoom, so you're not bludgeoned by scads of unnecessary information, and they rotate along with the map. Neighborhoods and regions are well-marked, and even parks and bodies of water take on a more attractive look. You can even adjust the size of the labels to be smaller or larger, and dictate whether they're always shown in English or in the native language of the location you're viewing.
That said, maps in some locales do not always perfectly reflect the environment. On a trip to some of the further reaches of Canada, for example, I noticed disparities between the geographies of the old and new Maps in terms of the shapes of certain landmasses. But in my experience, it was more of an aesthetic difference than anything else.
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