This extension does what is says, is easy to use and is flexible. The only drawback is that the title cannot be styled, so there is no visual indicator that the tooltip exists unless the user is lucky enough to hover the text. I like an innocuous dashed bottom border. There are workarounds, but I haven't found any that work with IE7 and earlier.
The title is wrapped in a div with a class called 'QToggle', So you can style the tooltip text accordingly with the stylesheet provided. If you want a dashed border the css would be this:
border-bottom: 1px dashed #CCCCCC;