Using image sprites is sort of a last resort after you have done as much as you can with other optimization techniques. A sprite is an image that has all of your other images inside of it, so if your sprite has 10 images, you'd be getting rid of 9 HTTP requests and speeding your site's loading time up by the time for each of those 9 requests' latency.
http://www.adamblacknow.com/tutorials/fix-thesis-css-for-aweber-button-sizes.html When making a custom form in aweber and using your own hosted button, thesis will override the css of the form and resize it to 45%. We want the button to be 100%.