As posted a few weeks ago, a recent US Chamber of Commerce commission, studying the problem of the Transportation Trust Fund starting to decline, floated the idea of levying an extra tax on hybrid vehicles to make up for the lower gas tax revenues expected from them.

How's that one for a great example of insightful forward thinking! What an incentive to go out and buy a hybrid!

If your state DOTs are anything like mine, at least a third of all road project expenditures is 100% pure grade A pork. That's where more attention should be focused, not where to squeeze the motorist next.

Yes, as a general rule, conservation will decrease governmnent tax revenues.  But that's quite easy to solve: the government can just raise the tax rates accordingly. Presto - more tax revenues magically appear.

One thing I am vehemently opposed to is some sort of black box that will automatically record how many miles you've travelled and then tax you accordingly. While such a system would make tax proportional to road use, it would only take minor modifications to morph it into a system that could tell a repressive government where and when you travelled. Does anyone want to be in position where he/she might have to explain to the police why you traveled 23.7 miles at 9:30 PM on January 17 to such and such coordinates?

 A good rule to follow is that if a new power can be abused, it will be abused.

This point about instituting a system so open to abuse by the state is a very important one IMO. It wouldn't surprise me at all if the the US, for one, morphed into a fascist theocracy in years to come. All manner of freedoms may be threatened as elites try to hold on to more than their share of a declining resource base by repressing the majority. A mileage charging scheme like the one proposed would certainly be a useful tool in the arsenal of a repressive state.
Ignorance is bliss and karma is what it is...................
That's for sure!

Plus such a system would be a perfect instrument for implementing enforced gasoline rationing.  It would be quite easy to configure the system so that the black box allows you to drive only X miles per week and then automatically disables your car. Or if the State determines that you have been a naughty boy, it could keep your car disabled for a certain period as a form of punishment.  

When my paranoid side gets the best of me (which seems to be happening more and more these days), I sometimes wonder whether this optional LO-JAC (sp?) system that is available on some GM cars is really a Trojan horse for the government to get its foot in the door to eventually make it mandatory for all new cars to have such a black box.

There is something to be said for keeping one old car with a points-and-condenser ignititon system: i) it won't be knocked out by an electomagnetic pulse in the event of a nuclear war, and ii) it can't be disabled remotely by a third party in the way that an electronic ignition can. In addition to my daily drivers, I just happen to have such a car: a 1968 Beetle. A great car for the Sixties, and perhaps a great car for the post peak oil Road Warrior scenario (after a few serious performance modifications, of course).  

If we're in the path of a nuclear EMP, there won't be many places worth driving to.
Tell that to Mad Max :-)
But Mad Max wasn't driving to any place--just endlessly searching for juice to feed the V8. I suspect the EROEI of that sort of cruising isn't very good. But it is a lovely lifestyle choice.
I really can't see that the government knowing [only] how far you drive is a big privacy issue. Just charge a flat rate per mile, check the odometer every time the car is inspected, and bill accordingly. This raises tax revenues, but does not give incentives to stay off of overburdened routes.

Note, though, that the UK is already proposing your worst-case GPS-based system, because they want to charge more for congested roads or peak hours, and less for lightly-travelled roads. To do this, they need to know exactly where you are, and when. The idea is to do two things: raise money, and change drivers' behaviour. It's an intrusive and high-tech way to make all roads into toll roads, with some charging higher rates than others.

Regardless of the implementation method, effective road taxes should reduce driving. And we will need to do that.

Not all states require car inspections.  If this becomes a national thing, there will have to be federal inspections.  Which will be a whole new layer of bureaucracy.
The car's computer could be programmed to record miles traveled without reporting where or when. Data could be collected at filling stations using RFID technology. Miles could be electronically billed to a credit card or bought in advance like we do for cell phones.