Load Google Maps API using jQuery Deferred.

load-google-maps.js

/*!
 * JavaScript - loadGoogleMaps( version, apiKey, language )
 *
 * - Load Google Maps API using jQuery Deferred. 
 *   Useful if you want to only load the Google Maps API on-demand.
 * - Requires jQuery 1.5
 * 
 * Copyright (c) 2011 Glenn Baker
 * Dual licensed under the MIT and GPL licenses.
 */
/*globals window, google, jQuery*/
var loadGoogleMaps = (function($) {
	
	var now = $.now(),
	
		promise;
	
	return function( version, apiKey, language ) {
		
		if( promise ) { return promise; }
		
			//Create a Deferred Object
		var	deferred = $.Deferred(),
		
			//Declare a resolve function, pass google.maps for the done functions
			resolve = function () {
				deferred.resolve( window.google && google.maps ? google.maps : false );
			},
			
			//global callback name
			callbackName = "loadGoogleMaps_" + ( now++ ),
			
			// Default Parameters
			params = $.extend(
			 {'sensor': false}
			 , apiKey ? {"key": apiKey} : {}
			 , language ? {"language": language} : {} 
			);;
		
		//If google.maps exists, then Google Maps API was probably loaded with the <script> tag
		if( window.google && google.maps ) {
			
			resolve();
		
		//If the google.load method exists, lets load the Google Maps API in Async.
		} else if ( window.google && google.load ) {
		
			google.load("maps", version || 3, {"other_params": $.param(params) , "callback" : resolve});

		//Last, try pure jQuery Ajax technique to load the Google Maps API in Async.
		} else {
			
			//Ajax URL params
			params = $.extend( params, {
				'v': version || 3,
				'callback': callbackName
			});
			
			//Declare the global callback
			window[callbackName] = function( ) {
				
				resolve();
				
				//Delete callback
				setTimeout(function() {
					try{
						delete window[callbackName];
					} catch( e ) {}
				}, 20);
			};
			
			//Can't use the jXHR promise because 'script' doesn't support 'callback=?'
			$.ajax({
				dataType: 'script',
				data: params,
				url: 'http://maps.google.com/maps/api/js'				
			});
			
		}
	
		promise = deferred.promise(); 
		
		return promise;
	};
	
}(jQuery));

sample-example.js

$(elem).on("myevent", function() {
  $.when( loadGoogleMaps( 3, API_KEY, LANG ) )
    .then(function() {
      !!google.maps // true
    });
});

// OR 

$(elem).on("myevent", function() {
  loadGoogleMaps( 3, API_KEY, LANG )
    .done(function() {
      !!google.maps // true
    });
});

I added libraries support in my fork