Eventually you run out of economical coal. This is an economics problem not a resource problem.
That is true. Already it costs more to produce coal than it did 20 years ago. The example in Peak Oil was that a carload of coal would produce 100 carloads of coal. Now it is: one carload produces 20 carloads of coal. Eventually people will start seeing past their own hood ornament and realize there are other cars, other houses, other cities, and even other countries. The problem is producing and distributing the energy resources--a monstrously hugh industry.
Actually the solution is coal gasification. The company is an American company called Hydrocarbon Technologies which is a subsidiary of Headwaters Incorporated. They have made a 2 billion dollar deal with Shenhua Group of China to build a plant. I believe the Shockwave Power technology is very similar to thermo-acoustic stirling engine technology that came out a few years ago (search for "Thunder in a bottle" on google). If President Bush announced this technology is being researched and then had the Secretary of Energy make the rounds on the talk shows, the oil producers would probably up their production to try and undermine it. Either way gas prices come down and our economy picks up. I'm sure methane or the solid methonates at the bottom of the ocean could be used.
It will take centuries to use up coal. Actually I mostly promote nuclear energy but this technology is pretty interesting.