As mentioned in this hint, Mountain Lion removed the setting in the Sharing preference pane to turn Web Sharing on and off, even though Apache Web Server is still installed by default. That hint also mentions a third-party preference pane that you can install to toggle Web Sharing in Mountain Lion.
Here's another solution in the form of an AppleScript. If you copy the script to a .scpt file in ~/Library/Scripts, you can conveniently toggle Web Sharing by selecting the script in the Scripts menu.
Here's the AppleScript:
display dialog "Enter your password:" with title "AppleScript" ¬ default answer "" with hidden answer set pw to text returned of result set resultMsg to do shell script " listResult=`launchctl list | grep org.apache.httpd`; if [[ $listResult ]]; then apachectl stop; echo 'Apache Web Server stopped.'; else apachectl start; echo 'Apache Web Server started.'; fi" password pw with administrator privileges tell application "Finder" set notifier to POSIX file "/Applications/Terminal-Notifier.app" if exists notifier then do shell script POSIX path of notifier ¬ & "/Contents/MacOS/terminal-notifier -message '" ¬ & resultMsg & "'" else display alert resultMsg end if end tell
The script uses the free Terminal-Notifier app by Eloy Durán, if installed, to notify you that Apache Web Server has been started or stopped. If you have the app installed somewhere other than /Applications, be sure to edit the app's path in the script.
Note that the state of Web Sharing is persistent across reboots, whether you use this method to control it or the aforementioned preference pane.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20120824214343458