Rounded corners are the bane of a website designer’s life. I can take them or leave them; for some reason, graphic designers seem to swoon at the slightest hint of revealed shoulder. And, while Mozilla has a CSS extension which does them, and CSS 3 standardises it, if you want them cross-browser then you used to be stuck with tables, or wrapping your divs in up to three others and using background images.
However, another alternative is script. If your site already requires JS, then you can now have lovely rounded corners in all modern browsers using a simple script and CSS include without the need for extra markup.