Look at some screen shots of the new Google Earth

Record your movement and voice inside of Google Earth
Look in the bottom left part of the 3D screen. Note the recording control. You can now record your movements and voice in Google Earth and then save them as a KMZ file.

Show the history of an area in the 3D viewer
World Trade Center now

World Trade Center 12-30-01

World Trade Center 9-11-01

World Trade Center 1997

Google has updated the timeline from 4.0. You can now easily go back in time and see what the earth looked like.