…for me the following did the job:

  1. cd /System/Library/LaunchDaemons/
  2. sudo launchctl load -w com.apple.screensharing.plist

where sudo launchctl unload -w com.apple.screensharing.plist would disable it. Worked for me in Lion. Might work in older versions too.

via 10.6: Start screen sharing remotely in Terminal – Mac OS X Hints.
Works also in Mountain Lion