An absolutely positioned CSS-based message box can be a useful design choice, but the same message popping up every time a user visits can get annoying. It’d be useful to give your users the ability to close those messages.
CSS doesn’t apply exclusively to the screen. You can also write style sheets that apply to the medium that first spawned them – print. And your layout may look stellar at 1024×768, but that doesn’t mean it rocks equally at 8 1/2″ x 11″.
Here's a great technique for creating old-school, book-style page/article introductions: drop-capped first letter, small capped first line. The technique uses pure CSS -- no divs, spans, classes or IDs are needed.