I don't mean to be the eternal skeptic, but as I understand it, all of these "clean burning" technologies only really work when they're running at 100% efficiency, which they rarely do in practice.

Other than that, the pollution and environmental destruction that would be caused by the return of coal as a major energy source has to be factored in alongside the emissions that are (or aren't) released when you burn the stuff.

As a peak-oil backup plan, maybe, but I don't think we can consider "clean coal" an environmental panacea by any means.