I went from a Hemi to a hybrid recently. I am now driving a Ford Fusion, essentially equipped the same way as our other unmarked police vehicles.
Since hybrids became popular, people constantly ask me about the application of these vehicles for law enforcement. I think it depends.
Manufacturers build "police package" vehicles to meet the unique demands of policing. The cars are not significantly different, but often include modifications to certain systems (electrical, cooling, braking, suspension, etc.). To date, hybrids have not been designed for police use and are vulnerable to the increased wear and tear experienced on patrol.
Although the prices have come down, hybrids are also more expensive than the police package vehicles sold to government. There are legitimate questions about whether the fuel economy equalizes the cost difference between the vehicles.
However, because there are more options available, I think hybrid vehicles might make sense for police administrators. The long-term costs are probably comparable to traditional "admin" cars and these vehicles are consistent with the City's "green" philosophy. I don't consider myself to be a champion of the environment, but there is something intrinsically more satisfying about burning and spewing less gas.
The Fusion has been a fun car to drive. The jury is still out, but I am enjoying the experiment.