Is there a comparison of networks and costs for iOS 4.3's Personal Hotspot?
The hotspot feature is, in essence, very similar to the Internet Tethering feature. The differences are that a) there's no cable required and b) you can connect up to 3* wifi-capable devices, so you're not restricted to tethering only devices that have USB or Bluetooth.
*See the below comments for the correct answer.
Jeff Carlson, writing in TidBITS, has a comprehensive comparison of the Personal Hotspot fees in the US for AT&T and Verizon. Even for non-US users, I think the article will be useful for its discussion of how the feature works.