I’ve noticed a few sites using full-width banners for important messages – the BBC for their webpage grandfathering:


and C4 for a parental warning:


There’s only one trouble. You just don’t see the banners. They’re in a position often occupied by adverts, and the extreme aspect ratio is similar to banner ads. There’s also something about the uniform height grid in the BBC example that really pushes the eye down the page over the banner.
I guess it’s a double-edged sword: you could use this specifically for large warnings that you have to include, but don’t want the user to pay attention to.
And a free bonus banner from Twitter:

You do see this one, as it transitions in from the top of the page, but it’s the most useless banner, as it prevents you from clicking on any of the top navigation until it’s gone.
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