I want to use it in the sidebar. Hovering the mouse pointer over the "Most Recent Posts" would result in large hovering tooltip showing an excerpt from the post. But this functionality could be useful for just about any list or sidebar item.
WordPress does produce a small "tool-tip" pop-up when hovering over list items but it this has two major weaknesses. First of all, the browser-controlled pop-ups are too small. Secondly, they contain the wrong info -- they repeat the post name instead of showing the post excerpt.