New Google Earth 4 beta - 16-December-2006
Google has just released the latest beta for Google Earth 4 today (December 16th). The Windows version is 4.0.2693, Mac is 4.0.2694. Here are the release notes posted by 'ink_polaroid' at the GEC. Note: there are some great improvements in here. Also, the new touring feature mentioned is really cool. It will automatically pop up placemark description bubbles as you tour through each placemark. This gives you an almost script-like presentation capability.

Release notes:
Progress indicator for loading network links and models
Real-time GPS tracking using NMEA (Plus, Pro and EC)
Greatly improved performance for collada models (textured buildings)
Tours can display balloons (Tools->Options... then "Touring" tab)
Driving directions and touring allow a greater range for typed values
Mac movie-maker supports many more compression formats
KML notes:

Icon palettes are deprecated (no more root:// for the styles)
Improved performance on network link hierarchies
Major fixes since last beta:

Improved compatibility on shared memory architecture ATI graphics cards with older graphics card drivers
Improved success rate of log in over unreliable connections
Fixed offline mode in Pro
Numerous GPS fixes (including GPX import)
The bug which affected the Blue Marble Add-on has been fixed. I will be posting a new version which won't require the little hack I had developed to fix the bug.