Google has ported Google Earth to the iPhone or iPod touch, and it's such an impressive app that it deserves an Apple ad of its own.
The interface for Google Earth will be familiar instantly to anyone who has used an iPhone for more than a couple of hours. Upon launching the app, you see a photo of the Earth from space. To zoom in, you can either double-tap or use the "reverse-pinch" gesture on the screen. Swiping a finger left, right, up, or down moves the display in the chosen direction, and a two-finger rotation turns the display clockwise or counter-clockwise. There are icons on the display (see screenshot at right) for search, using your current location, changing settings, and realigning the display to North.
Things get more interesting when you tilt your iPhone; the display goes from a flat, satellite-eye view to a 3D-like image. If you're near mountainous terrain, you get a true sense of the topographical features of the land. On many screens you'll see Wikipedia icons, which link you to related Wikipedia articles. Read the rest of this post for more details and a gallery of screenshots.
Tapping on the location icon in the lower left corner of the display turns on geolocation, and I was amazed at how accurate this was -- it was basically floating the big blue pin right over my home office! I had to avoid the temptation to look out the window and see if the pin was there.
The imagery consists of the same satellite and aerial photography that you'll find on the Mac or PC version, so if your area has low-res imagery, don't expect to see something better on the iPhone. You can add a Panoramio layer to view geo-located photos, or search for locations using a built-in search function.
One thing I noticed with this 1.0 release is that it tended to crash quite frequently, most often when I was looking at a zoomed-in image of something near a 3D surface and then tried to tilt or pan the image. Restarting the 16GB iPhone 3G didn't seem to help matters at all. Until Google fixes this issue, try to avoid the coolness factor of tilting your iPhone for that 3D viewpoint.
As with most things Googlish, Google Earth is free. The app is localized in sixteen languages, and is available from the App Store (click opens iTunes). If you have an iPhone or iPod touch, be sure to download Google Earth just for the sheer fun of it, then let us know what you like or dislike about the app.