The term's been popping up a LOT lately, so I thought I'd give a few links to pages worth reading (there's not much point me re-doing it, it's already done so well)
Steve from Rising Tide Newcastle has written a clean coal fact sheet, with a lot of good stuff about carbon capture and storage. Check it out, and leave comments if you want.
There's also a good piece on the HCEC website, showing that coal will probably run out before "clean coal" is even viable, at least in the Hunter.
There's some good arguments at mindfully.org, by Vivian Stockman, from the Ohio Valley Environmental Coalition.
Of course, Greenpeace has a good shot at it too, with their myths and facts sheet.
There's hundreds more out there. if you find any good ones, or ones that point out something that the above articles have missed, leave a comment with a link.