The industry professionals at The Oil Drum suspect that the real leak in the Deepwater Horizon site is not at the blowout preventer, but 1,000 feet below the sea floor. BP may have even been trying to increase the flow at the sea floor to relieve pressure on the leak 1,000 feet below.
The post is full of technical industry talk (and rather badly edited) so it is hard for me to figure out exactly what they are saying, but there seem to be two further catastrophes to fear. Apparently the sea floor there is just silt that doesn't really provide any support for the blowout preventer. The preventer is just resting on the 1000 foot pipe beneath it, which now seems to be buckling. The other problem is that the sea floor itself might be opening up, causing the whole oil reserve to come to the surface at once. I'm not sure how this outcome is compatible with the worry about the pipe collapsing, since it seem to imply that the sea floor is a solid mass that can shatter, which they just said it wasn't. I'd like to see more explanations of this stuff.
Update: Prof. Goose from The Oil Drum has stopped by Unfogged to explain some things http://tinyurl.com/3xunewu. He points out that the article is by a TOD commenter, not a regular writer. Goose points to comments on The Oil Drum thread that undermine dougr's original post. A guy calling himself R2-3D points to other signs that would be present if there had been a casing blow out beneath the sea floor. Maybe we should leave this to the experts to debate before we reach higher levels of panic than we have currently.