Hi jjdoc,
From my understanding, the Prius is better at stop and go traffic in comparison to the 2005 Civic Hybrid due to the differences in their hybrid power trains. Basically, the Prius has the 'idle stop' feature like the Civic (when you stop for a period of time, and the environmental controls are set to 'off' or 'econ' the internal combustion engine turns off). In the Civic hybrid, the ICE will restart when you take your foot off the brake and accelerate. However, the Prius is different in that instead of the ICE (the gas engine) restarting, the electric motor is able to propel the car forward, sometimes up to speeds of around 30-40
mph. The Civic (2005 model) cannot do this. It gets its best mileage on the highway, at constant speeds.
Apparently the 2006 model of the Civic hybrid will address this, and be able to drive for a bit using only the electric motor (when running on electricity only, you obviously don't burn fuel). It sounds as if the 2006 model will be more comprable in terms of the drive train to the Prius than the current Civic incarnation. As for your HOV questions, I can only speculate that it will probably be eligable. To my knowledge, the current Civic Hybrid is eligible, and the 2006 will be more efficient, and have better emissions controls. If I am wrong about any of this, perhaps somebody can let the both of us know. Hope this helps!