The iPad's large screen gives Google Earth a distinct advantage over using the app on the iPhone. Navigation and tilt are much easier to use and the app is much snappier overall. The large screen touch capabilities also makes it feel like you are holding a fully-interactive globe in your hands. The only feature I wish they would add is a "North-lock." It would be great if you could spin the Earth at a specific orientation without it rotating all over the place.
Google Earth 3.0 for iPad, iPhone, and iPod touch is available for free in the App Store.