Any appreciable amount data should never be lost. That is what backups are for.
The ability to get snapshots without shutting down the fs is a very important widget in the fs toolset. I find it geekily exciting[for lack of better phrase] that such a great tool will be available for OSS. One cannot, should not, rely upon any other means than a backup to protect data. All the other methods are there, IMHO, to keep from having to restore data because restoration does not always go as planned and backups are only as good as the last backup set. If we open source users can copy on write (CoW) and get snapshots without interfering with computing tasks, ...wow!

[snip JFS(JFS2) is oh so much better than ext* stuff]

I appreciate the benchmarks posted here despite the shortcomings(e.g., they are "canned benchmarks"). I do wish they would include JFS and ZFS also as well as perform the critical tasks like fsck for those four but if not I will prbly find out on my own, ...unfortunately.