Post thumbs on your home page or category archives look very snazzy. Here is a function you can put into your theme functions.php and call it in your index or archive templates, to show the thumbnail image extracted from the post. This is a quick and simple hack. The function will just get the url of the image, or in case you use Smart Youtube plugin the representing image of the video. That means you still need to resize it with CSS or create and save thumbnail.