Now that iPad 4.2 beta 3 has been released, reports are coming that Apple has removed the tethering settings. As you can see in the screenshot below, tethering options are no longer present under the "Cellular Data" fields.
"Tethering is the use of a mobile device with Internet access such as 3G cellular service to serve as an Internet gateway or access point for other devices. Other devices may connect to the gateway via Bluetooth, Wi-Fi or by Universal Serial Bus (USB) cabling.
Tethering uses mobile applications or software depending on the mobile's operating system. A popular application is Joikuspot that works on Nokia(Symbian), Samsung and Windows Mobile phones," Wikipedia.