I really question whether hybrid technology is effective for over the road vehicles that do mostly highway driving.
It's not, which is why you don't see any over-the-road haul truck hybrids. A promising technology is electric drive, but not as a hybrid. Rather as RVRoamer pointed out, diesel-electric drive, similar to what locomotives use, is being tested. Basically, you use a high-efficiency combustion engine running at peak efficiency to generate electricity only, then apply that electricity to charge a battery and to drive motors (I should note that locomotives don't have batteries and bleed off regenerated electricity from their traction motors using resistive heaters to get rid of the energy instead of storing it in a battery). This is the concept being explored by the Chevy Volt and has the potential to yield relatively significant improvements in over the road efficiency as well as around-town improvements.
BTW, batteries in Hybrids have been proven to be one of the most reliable components of the drivetrain. The average NiMH battery in today's hybrid will last as long as the chassis/drivetrain, or roughly 150,000 miles. This is not theory, it is fact, and is supported by battery orders by Honda and Toyota hybrid owners, which is averaging less than 2 per 100 vehicles. There is now over 10 years of real-life evidence to support that battery life is not an issue.
That said, battery use in an over-the-road vehicle with an expected life of much more than 150,000 would obviously be quite different than in a passenger car and replacement would have to be considered in the life-cycle costs of any design. LiON batteries could be an improvement here but the technology is proving to be much more difficult to apply in real-world vehicles than GM, Toyota, Honda, or BMW expected, hence the delay in production Hybrids utilizing them.
The other benefit to electric drive vehicles is the potential to utilize "trolley assist" which involves using an outside power source for the vehicle (think of an overhead electric line, or an embedded electric rail in the highway) to avoid using the engine at all.