In general, I keep all spares zeroed; it's a low-impact operation and its a handy convenience. actually, I'd like to see an option that auto-zeros spares when they are inserted, so I never need to do it manually.
Skottie, I agree with you for the most part. I zero my spares when I destoy a volume after a couple of days. However, I *don't* want it done automagically. One time (thank goodness) I thought I was going to have to work with NA to restore an already destroyed volume. Had the spares been zeroed I would have been SOL. I like having control of when they zero personally. Not sure how the rest of the world feels about it but I like being able to push the button.
I also know of a bug that caused disks to be seen as spares after an upgrade. Auto-zeroing was a really bad thing for that customer because after the upgrade all the disks seemed to be spares (even though they weren't) and the filer zeroed the disks. It was a long time ago so I don't remember the exact details. All I do know is that restoring from tape stinks. ;)
Just my 2 cents. C-