While you cannot get the focus to follow the mouse from one application to another, it is possible to achieve this within an application:

• Apple Terminal -- from the command line, run:

         bash$ defaults write com.apple.Terminal FocusFollowsMouse -string YES

• xterm -- from the command line, run:

         bash$ defaults write com.apple.x11 wm_ffm -bool true

Quit the application to save it and restart it to apply it to any new Apple Terminal/X11 windows. Typing

         bash$ defaults write com.apple.x11 no_quit_alert

into an x11 window (quitting, restarting) will also allow you to log out if X11 is running

-- DarrellSchiebel - 17 Jun 2005