If you have a need to enable or disable Screen Sharing from a terminal in OS X the commands are very simple. I’ve used these commands in 10.6 (Snow Leopard).
sudo touch /etc/ScreenSharing.launchd
sudo rm /etc/ScreenSharing.launchd
Updated 06/07/2012: It seems that the process for doing this has changed in OS X Lion based on a post in Ryan’s Tech Notes. I used these commands and they worked as described.
sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -activate -configure -access -on -clientopts -setvnclegacy -vnclegacy yes -clientopts -setvncpw -vncpw mypasswd -restart -agent -privs -all
sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -deactivate -configure -access -off