USS San Francisco Information
It looks like the Navy hasn't released any new reports on the San Francisco grounding discussed below, so all that's floating around now is just idle speculation. I saw on some of the more "uninformed" bulletin boards some posters theorizing that the San Fran had maybe collided with a Chinese submarine, rather than with the bottom. This was based somewhat on the reports that the Chinese submarine that had intruded into Japanese waters (discussed in this blog here) had earlier been tracked by the U.S. Navy near Guam. I find this conjecture highly improbable, for the simple reason that we probably wouldn't have released the news of any damage to the San Francisco if it had happened due to a collision. As far as speculation that the San Fran might not have heard the Chinese sub -- well, any sub that a P-3 can track can definitely be detected by a submerged submarine.
Here is the official Commander Nav Base Marianas page on the San Francisco that has some decent background information.