This is how I'm using TypeKit in the Rails asset pipeline. Replace your kit id, of course.

gistfile1.js

(function() {
	var head = document.getElementsByTagName('head')[0];
	var script = document.createElement('script');
	script.type = 'text/javascript';    
	script.src = '//use.typekit.net/XXXXXXX.js';
	var callback = function() {
		try {
			Typekit.load();			
		} catch(e) { 
			// report error			
		}
	}
	script.onreadystatechange = callback;
	script.onload = callback;
	head.appendChild(script);
})();