Designers who pop up information panels or move page elements on hover are using flawed logic, second-guessing what users want to do before they do it. The result, which I’ve seen in countless usability tests, is that users activate these controls accidentally. You know what happens? People actually flinch: “What was that?” They return with hesitation, less confident in their understanding of the site. It’s no accident that the Twitter worm propagated through hover—accidental activation meant users spread the worm unintentionally.
via Cennydd Bowles – End hover abuse now. A call to action for designers to stop over using the hover attribute.
Should mention at the end the designer goes back and says that if you are to use hover to show new information to add a 500ms delay before firing the action. I’ve seen and implemented hover states to display new information and I think it’s a useful technique with a well defined use case, the problem does become one of people having a correct and valid mental model for the website and how it works. Hover actions can quickly break that model.