Create Elements using memoization technique (modified to @GarrettS' points) #js

createElement.js

/**
 * The following method creates a new element or returns a copy of an element already created by this script.
 *
 * @param tagname { String } element to be created/copied
 * @return { Element/Node } the newly created element
 */
createElement: (function(){
	// Memorize previous elements created
	var cache = {};
	
	return function(tagname) {
		if (!(tagname in cache)) {
			// Create new instance of specified element and store it
			cache[tagname] = document.createElement(tagname);
		}
		
		// If we've already created an element of the specified kind then duplicate it
		return cache[tagname].cloneNode(false);
	}
}())

Shallow cloning one element won't do much.
http://jsperf.com/clonenode-vs-createelement-performance/2
Except for img elements in Firefox 7, it looks like the benefit could be explained by setting the property again.

The extra function dependency in the codebase must be maintained and downloaded. Just document.createElement is simpler.