Everything I've seen on the US Cellular website indicates they want to charge for tethering. I've only tried once, on my Desire with a USB cable, and it asked for a password (which my local provider offered for the tethering fee).
From their site as of today:
Android Tethering Instructions | Smartphone Modem Feature | Android | U.S. Cellular
Android Downloads | Android-Powered Phones | U.S. Cellular
You can use your AndroidTM-Powered phone as a modem to access the Internet from your PC. To take advantage of this tethering feature, you must have an APPROVED DATA PLAN associated with your account. Here are the details of the data plan you'll need when using your phone as a modem:
Data Plus (5GB data usage per month)
Overage billed at $0.25/MB (capped at $200 maximum per month)
TETHERED MODEM SERVICE IS AVAILABLE ON THE FOLLOWING PLANS
With Android 2.2. anywhere between 5-8 users can connect to U.S. Cellularís network through the Mobile Hotspot. Being able to share a 3G Web connection with other users will undoubtedly come in handy in a professional setting when a team needs a Web connection.
Note: This feature requires a tethering plan