With Google Earth, to rotate the view in 3D space, you use the middle-mouse button. You also need to imagine that there is an invisible sphere, about 60% of the size of the viewport, which your cursor is dragging and rotating, which in turn rotates the globe. This is confusing and not the most intuitive, since it effectively reverses the direction of rotation depending on whether the cursor is in the northern or the southern hemisphere of the sphere (not the globe we see on-screen).
Worldwind is more like the controls of a 3D strategy game. Right-click (easier to press and hold IMO) controls 3D movement, and the rotation doesn't suddenly reverse direction if you move from one "hemisphere" to another.
The main reason I use Google Earth as opposed to WorldWind is because of the servers - Google's servers are always ready to stream data at decent rates; NASA's servers often seem overloaded. However, despite the 175Mb download that WorldWind is, if you're on broadband, it's worth it to at least check out - it has the advantage of far more pure data at your fingertips - MODIS, LANDSAT, etc etc etc. It's far more... scientifically appropriate.
Google Earth just works.
