If you have a Windows Phone 7 you are in for a treat!
I just ran an updated (literally 3 minutes ago) on my HTC HD7 and it now has Internet Sharing! It option wasn’t under the WIFI setup screen like I have seen in previous screen shots on the Microsoft site. Instead it is an option under Settings called Internet Sharing.
Keep in mind T-Mobile has a 2GB/month quota and anything over that is slowed down. I’ve never hit the cap with my smart phone even with Netflix. I no longer have Netflix but now with tethering I can see the potential of hitting the threshold. Happy day WP7 phone users!