Comment 5 for bug 542378

No, I have no ntfs partition. The one I can't mount is '/', of type ext4 (see grub.cfg entry above).

What I have noticed is that if I get the 'waiting for / [SM]' message, and select M then ctrl-d, booting continues correctly.

This suggests to me that the filesystem ('/' in my case) did in fact mount correctly, and it is just that mountall or plymouth never noticed.

This makes sense; both mountall and plymouth are new. This bug is also intermittent for me, which suggests a race condition. Mounting drives is old and established code, so a race condition is unlikely. The new code for *detecting* that the mount has happened, however, could well be racy. (warning: pure speculation)