Hybrid vehicles - those which operate through a combination of a traditional internal combustion engine and an electric motor - promised much in terms of fuel savings and reduced environmental damage to a contemporary society which remains mostly dependent on small ground vehicles for its transportation. However, it is important to remember the so-called "hybrid fallacy": both in terms of cost and reduced environmental damage, the hybrid vehicle can be beneficial, but not so quickly or so impressively as might first appear.
The most important feature of the hybrid car, from a long-term perspective, is of course the promise of a reduced ecological footprint - or, in other words, less environmental damage done by each vehicle and by each mile driven. However, it is important to remember that here, too, the hybrid car is more an incremental improvement than a radical restructuring of the automobile industry.
The first reason for this, of course, is that the fossil fuels consumed by driving are actually only one of the important factors which go into determining the overall ecological impact of a vehicle. A substantial portion of that impact, however, is also accounted for before the vehicle is even driven off the lot. Building a modern car requires producing and assembling a considerable mass of metal and plastic components. This is why the Obama administration's so-called "Cash for Clunkers" program was also questioned by environmentalists, for example.
Moreover, and most importantly, it is important to combat the greatest part of the hybrid fallacy: the potentially misleading belief that electrical energy is necessary clean energy. This is certainly true in the case of incremental improvements to vehicle efficiency by new technologies like regenerative braking. Overall, however (and this will become even more important if there is a transition to fully electric vehicles in the future), electricity still must come from somewhere, and if the energy to drive the car is not produced within the vehicle itself, then logically it must come from somewhere else. Centralized power production is necessarily more efficient and thus less polluting than dispersing hundreds of millions of small combustion engines into vehicles all over the world, of course, but so long as countries remain heavily dependent on fossil fuel resources like coal, growing reliance on electric motors doesn't necessarily reduce one's environmental footprint: it simply shifts the source of pollution from the automobile tailpipe to the power plant smokestack.