There have been a lot of the same arguments (and more than few misconceptions) that have been made over and over again in this thread, so I've created a rather long blog post, "Don't fear the fsync!", which will hopefully answer a number of the questions people have raised:
It will probably be more efficient to attach comments to that post than to add more comments to this (already extremely long) Launchpad bug, since many of the comments are discussing philosophical issues, and as some folks have already pointed out, patches to deal with forcing out blocks on rename (just like ext3 does) have already been backported into the Ubuntu kernel, and will be in 2.6.30. I understand that btrfs will also be adding an flush-on-rename patch in 2.6.30. (Note that XFS at this point only has flush-when-closing-previously-truncated-file; which yes, I implemented after Eric Sandeen from Red Hat pointed out XFS had done. However, XFS does not, as of this date, flush-blocks-on-rename behaviour --- this was my innovation, to reward applications that were at least making an attempt to do things right --- although given the notoriety of this discussion, I wouldn't be surprised if Eric or some other XFS developer also adds this to XFS for 2.6.30).
However, if you are an application writer, please, please, PLEASE read my blog post "Don't fear the fsync!".