I have - twice. And both cases were validated HTML 4.01 strict and validated CSS.
Well, the page did work on IE7 and only had problems on IE8. Compatibility View fixed it, but that's small comfort. No other browser we tested on XP Pro, Vista or OS X had trouble - not Opera, Safari, Chrome, Firefox. And one of these issues was not a small nitpick. It blew up the header section layout! We ended up mystified and had to drop the "Home" link on the business logo.