Well, this is different. ASRock has introduced a couple of new motherbards designed specifically for Bitcoin mining. Both are loaded with PCI Express slots for discrete graphics cards. They also have auxiliary Molex connectors that provide additional power to those expansion slots.
The H81 Pro BTC pictured above offers Haswell compatibility via Intel's H81 Express platform, while the H61 Pro BTC works with older CPUs. Each board has one PCI Express x16 slot tied to the CPU in addition to five x1 slots presumably linked to the chipset. Oddly, the x1 slots aren't open-ended to accommodate full-sized graphics cards. It looks like you're supposed to use a PCIe ribbon extender to interface with multiple graphics cards.
Apart from the slot arrangement and additional power connectors, the boards are pretty unremarkable. The H61 variant doesn't even have USB 3.0 connectivity. Note that these are ATX boards with unconventional dimensions. Most motherboards based on the H81 and H61 platforms have smaller microATX footprints—and fewer expansion slots as a result.
We don't yet know pricing or when the BTC boards will hit the market. There's also no guarantee that mining will generate enough revenue to cover the cost of a dedicated rig, let alone the electricity needed to power it. The concept is interesting, though, and these BTC boards might make good foundations for Folding@home machines.