When we ask the question about synthetic fuels from coal, we should ask the question of what is the ultimate objective and what is the most cost effective, most energy efficient and least environmentally damaging method of achieving that objective. Why do we want to produce petrol? We need petrol as it is a convent and portable energy source that can be used to power vehicles. So when we convert coal into petrol, the petrol is nothing more than an energy storage medium. As was pointed out above coal-to-liquids is a very inefficient and extremely energy intensive process. It would probably be much more economical, more energy efficient and less environmentally damaging to simply convert coal into electricity, which could be delivered to the consumer via existing infrastructure and stored in the vehicle via either chemical batteries (e.g. lithium ion) or fuel cells (e.g. hydrogen).
Another advantage focusing R&D efforts on electrical energy storage is that the technology is not beholden on just coal. Any energy source that can be used to generate electricity could be used. This includes point of use generators like solar panels on consumers' homes. Our best short term hope for reducing the need for crude oil based energy is plug-in hybrids. Plug-in hybrids would allow vehicles (e.g. passenger cars) to be mostly powered via batteries (or fuel cells), with petrol only being used for longer trips. Since most drivers drive less than 35 miles per day even existing battery storage technology can handle most driving needs.
One great advantage to plug-in hybrids over coal-to-liquids is that because these vehicles would be mostly charged at night, when demand on the electrical grid is at its lowest, it is estimated that the current U.S. electrical production capacity could handle up to 75% of the U.S. vehicle fleet being converted to plug-in hybrid WITHOUT adding new power generating capacity.
This is not to say that there wouldn't come a point in time where we might need to begin to convert coal-to-liquids to power things like jet turbines of aircraft, but that we could simply limit the consumption of CTL petrol to those uses that CAN NOT be powered by stored electric power.
We should also remember that CTL is no magic bullet to our dependence on crude oil. By the coal industry's own estimates it will cost around $200 billion and take 20 years to build enough CTL capacity to replace just 10% of the current U.S. crude oil needs. Plug-in hybrids on the other hand could probably replace this amount of crude oil needs within a few years for a fraction of the cost and would save the consumer considerable amounts of money in terms of recurring energy costs.