Drawbacks

Although an improvement in convenience over electric vehicles, hybrids still cause more emissions than electric ones do.  It is important to note however that the true level of emissions of electric cars depends on the source of the energy used to recharge the battery.  Currently this energy source is often coal power plants, in which case recharging the battery results in some emissions.

Hybrid cars are superior or comparable in every respect to conventional cars, but are currently often more expensive up front.  Usually reduced fuel costs due to the hybrid's better efficiency will make up for this.

Because they contain a combustion engine, hybrid vehicles reduce but do not eliminate automotive emissions.  Thus their benefit is limited to lessening the severity of automobile air pollution rather than wiping it out.  See "Future of the Automobile Industry" link to the left for more on this fact.

Sources:
http://www.care2.com/channels/ecoinfo/hybrid