If you've got a bad case of insomnia, Microsoft has 943 pages of specs to bring on the shuteye. That's the size of the PDF with the set of hardware requirements for tablet manufacturers that want to sell a Windows 8 tablet.
There are three PDFs total, for PCs, one for devices, and one for "filter drivers." The devices PDF, which is for tablets, is easily the largest and goes into extremely minute detail, so I'll bottom line it for you.
Any Windows 8 tablet has to have five control buttons: power, rotation lock, Windows key, volume up and volume down. The minimum native resolution is 1366x768 although it can be greater, and with a 32-bit color depth. The physical dimensions of the display panel must match the aspect ratio the native resolution. 
Graphics need to be Direct3D and the camera must be 720p quality at a minimum. Accelerometers, magnetometers and gyroscopes are all required, as are USB 2.0 ports, WLAN and Bluetooth 4.0.
Tablets will get their own equivalent to the venerable Ctrl+Alt+Del key sequence even though there is no keyboard on a tablet. For Windows 8 tablets, the new panic button is a combination of the Windows Key button and the Power Button.
Windows 8 tablets will need to have at least 10GB of free storage space "after the out-of-box experience completes," which would be after unboxing and the device is run for the first time.
Near-field communication (NFC) support is also a requirement, with Microsoft requiring an external marker for showing where the technology is embedded. NFC specs are detailed in the PDF.
On the PC side, there are some interesting revelations. UEFI isn't just being supported, it's being mandated. You must use UEFI, not the creaky old BIOS that is currently used in pretty much every PC on the market.
Microsoft defines a tablet form factor is defined as "a standalone device that combines the PC, display and rechargeable power source in a single chassis. A tablet does not include a permanently attached keyboard and pointing device but can be connected to a port replicator, keyboard and/or clamshell dock."
A convertible form factor is defined as "a standalone device that combines the PC, display and rechargeable power source with a mechanically attached keyboard and pointing device in a single chassis. A convertible can be transformed into a tablet where the attached input devices are hidden or removed leaving the display as the only input mechanism."
Looks like that beta is rapidly approaching.