AjaxRoundEffect is a wrapper around the Rico rounded-corner CSS modifier. AjaxRoundEffect can be used in two ways. In the short-cut style, it acts as a WOComponentContent that will declare a "div" and class on the fly for rounding. If the rounding settings are to be reused on multiple elements, then AjaxRoundEffect should be declared at the bottom of your page (below anything it will round) with no content in it. AjaxRoundEffect actually modifies your CSS style definitions on-the-fly. As a result, it should only be used one time on a page for each CSS class that is being modified. If it is applied multiple times, you will get strange double-corners.
A demo of the Rico rounding effect is available here.