Three things:

• Avi Bar-Zeev, one of the original programmers on Keyhole Earth, which became Google Earth, has some insightful commentary on on Google Earth for iPhone, including:
  

  I’m not too surpried about performance. It reminds me of how the original Keyhole app ran on unaccelerated laptops. Without terrain, the number of triangles shouldn’t be the limiter (you only need about 1000 triangles to make a nice sphere). Texturing, caching, and download speeds seem like they would have been the biggest challenges.

• After a few hours of using Google Earth for iPhone, I’ve concluded that the easiest way to navigate is by holding the iPhone sideways and then using both thumbs on the screen. Pinching/zooming and twisting/rotating becomes even more intuitive, and you have a better view of the screen. Also, a wide screen gives you more room to read labels, which are always horizontal in Google Earth. (Horizontal labels are still my favorite usability advantage over over Virtual Earth 3D, where labels remain hard-coded into the map, which means they are upside down if you are looking South.)
• Technological advance is a wonderful thing. Who’d have guessed even five years ago that before this decade was out I’d have the ultimate 3D atlas in my pocket. Even more remarkable perhaps is how smoothly we adapt to new gadgets that until very recently were in the realm of science fiction. Still, I’ve caught myself several times these past 24 hours with a “wow” on my face, amazed at where technology is taking us. I’m glad I’m still able access my boyish sense of wonder:-)