I just ran across an excellent article entitled Why “left: -9999px;” is Better For Accessibility Than “display: none;”. It discusses the two primary means by which web developers try to hide text (usually to allow for accessible logos or titles), and why using an offset is (often) better than just simply making it invisible. The author also explains why this is better, using some documentation from Microsoft on Internet Explorer accessibility. Looks like I need to fix my websites!