The kate moss of stacks: flat, fashionable, and almost Responsive.
This is how Windows does Metro-style tiles — they may not be particularly subtle but they do make a great impact on modern, flat and responsive designs, and make really good product tiles, link boxes, and footers so trendy they draw blood. Click one and see. As you can also see below, you can use them to make great flat social icon buttons by simply adding a Bigfoot IconThing (or any other icon) to the tile.