1. Download and install the action.
2. Create a new workflow in Automator containing only the Display Notification Center Alert action.
3. In the variables section at the bottom of the workflow construction area in Automator's window, create three variables named title, subtitle, and message.
4. Give message a default value like "Notification sent." You can leave the default values other two blank.
5. Drag each variable to its corresponding field in the Display Notification Center Alert action.
6. Save the workflow as Display Notification.wflow. A good place to save it is in ~/Library/Workflows (create the folder if necessary).

Now you can display a notification from the command line using the following command:
automator -D title='Title text' -D subtitle='Subtitle text' -D message='Message text' ~/Library/Workflows/'Display Notification.wflow'

To display notifications from AppleScripts, paste the following handler into your script, and call it using the form notify("Notification title", "Notification subtitle", "Notification message")

on notify(title, subtitle, message)
	if title as text is not "" then set title to " -D title=" & quoted form of (title as text)
	if subtitle as text is not "" then set subtitle to " -D subtitle=" & quoted form of (subtitle as text)
	if message as text is not "" then set message to " -D message=" & quoted form of (message as text)
	
	do shell script "automator" & title & subtitle & message & " ~/Library/Workflows/Display Notification.wflow"
end notify

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.