Just to put another point of view...

I have been using venti at work and at home, and I have no UPSs (UPI ?).
As yet (touch wood) I have only ever lost a maximum of days work, and this
was due to a disk failure taking out my fossil drive which I don't bother
to mirror.

I have never had any data corruption or loss in my venti archive.

Perhaps this is because I only write to it using fossil snapshots at 4am
and not using vac - so the window when the system is vunerable is smaller.