Don't tell Verizon, but I got (fairly basic) tethering working over USB with my shiny new Droid. The instructions are available at the TetherBot site, and work quite well.
A quick speed test shows that I'm getting basically the full speed of FiOS (my home ISP) when tethering using the Droid's WiFi (10Mb down, 2Mb up), and a respectable 1.2Mb down and 0.44Mb up when using Verizon's 3G wireless data. Not bad.
Of course, since the Droid can do nearly everything I would want my laptop to do, I don't see much of a reason for tethering, but it's nice to know that the possibility exists.