I have noticed this problem and discovered that the tether app is slightly touchy. It works if you first turn on your phone and activate the tether app and LEAVE IT RUNNING ON SCREEN, PLUG IT IN SO IT DOESN'T TIME-OUT. If you deactivate and re-activate the tether it WILL NOT WORK ANYMORE and you will have to restart your phone and do it again. I have also noticed that you have to restart your phone if you want to return the phone back to normal 3G usage.I've got a DX, just DL'd the most current version of Wireless Tether (pre-14), and still have this problem. My computer recognizes and connects to the phone wirelessly, but 95% of the time it's either "Limited Connectivity" (meaning, no internet) or literally just says "Local" only. Access Control is not checked.
Any other thoughts?
Also, the tether app doesn't connect/work unless you install Droid X Bootstrapper and install the .zip to correct the problems since the Gingerbread update took away this free tether feature: http://www.droidforums.net/forum/droid-x-hacks/191891-tethering-2-3-3-a.html