Hello,
new here but wanted to give some feedback on tetherbot...
It's ideal for what I wanted: forward a single port to a fixed address.
It works fine on Milestone with the recent Android 2.2.1 official ROM.
This ROM has usb tether disabled by motorola (in France at least). Thanks motorola

.
I use tetherbot with this setup:
1) start tetherbot tunnel pointing to my server on port 443
2) start adb forward
3) run openvpn (configured on tcp only) on PC pointing to localhost
and that's it.
I can connect through my phone (and bypass all the limitations of my data plan

). It seems to work fine speedwise.
Thanks a lot Graham!
PS: the software seems difficult to find unlike other stuff that does not work as well but is on the market... Did Graham/anyone consider putting it there? Thanks