Although I've never used any of the info in the tooltip, I can see how it might be useful to some people. My main gripe is that it obscures other data when I run the mouse cursor over the list while scrolling.

Perhaps an idea would be to make the tooltip pop up only for items after they've been clicked on or make the info appear in a separate info panel (like the status bar in many Windows apps changes depending on the menu option the mouse is currently over -- or it displays the URL of a link when hovering in your browser).

Just the option to switch it off (or maybe 3 settings: none, simple, full) would be terrific IMHO.