ClockworkMod, aka Koushik Dutta, a favorite among the modding and hacker crowd because of great apps like ROM Manager, has released a very alpha version of Clockwork Mod Tether, and no-root required application for Android that will bring USB tethering to Windows, Mac and Linux. Koush seems pretty confident that he has worked out a solution that will be invisible to your carrier by using a virtual network interface on your computer that acts as a network proxy. It's worth mentioning that your network data caps and speeds will still apply, you'll just be able to use that data on a computer as well as on your phone or tablet, without the carrier knowing that's what you're doing. Dumb pipes FTW.
This is a very early preview, and may very well have some issues -- which is why Koush is soliciting alpha testing -- and there's no support or instructions for use yet. If you feel like having an early look, and are willing to help in the development, watch +Koushik Dutta for details.
Source: +Koushik Dutta