Update (6/25/10): The consensus at The Oil Drum is that dougr's post is highly flawed. I think that this was not quite so obvious when I wrote this post and an earlier one, but since then it has become clear that there are no cracks in the seafloor, and no oil is escaping from the seafloor around the riser pipe. Yesterday another Oil Drum poster provided a much more detailed and knowledgeable takedown of dougr's post.
Emptywheel and Zero Hedge pick up on the possibility that the BP well is damaged below the sea floor. Emptywheel's source is primarily Florida's Senator Bill Nelson, whose staff presumably is providing the information to him. Zero Hedge quotes MSM sources, Nelson, and petroleum experts, one of whom is Matt Simmons. Commenters at The Oil Drum seem to be discounting Simmons.
I'm rethinking yesterday's post on the worst case and find it less alarming. Fast flow, particularly of supercritical fluids flashing to gases, which may be happening in the formation, is as likely to deposit dissolved matter and plug up the formation as it is to erode it. I also suspect that the relief wells are designed to intersect the existing well below any casing damage that may exist.