Modal dialog boxes, i.e. windows/dialogs that once opened must be closed before the user can continue, have always been a bit of an usability no-no.
The biggest problems being that the user either doesn’t notice the modal dialog has appeared, or doesn’t realise that it requires their attention before they can continue.
As you can see from the above example on the BBC’s site, the Lightbox technique leaves the user in no doubt what they need to do before they can return to the main window.
I haven’t yet conducted any usability testing on this kind of Lightbox dialog, but my guess is that it will test far better than traditional modal dialogs.
I see that Jakob Nielsen named the Lightbox his “interaction design technique of the year” in his Year’s 10 Best Application UIs 2008. Nice to get there before the Dane.