No personal knowledge, but I've heard from three independent sources that yahoo is a large and satisfied netapp customer. Probably less so now than in the past (tighter market conditions, more reasonably priced alternatives than existed in the mid-late 90's) but snapmirror is rather nice for critical data centers. We are quite happy housing our Oracle databases on a netapp. If you're on a budget and can tolerate risk, do your hot backups from linux lvm snapshots. (ACS is read-mostly, though... I don't know that there's any ACS site with such churn that you couldn't leave the db in backup mode long enough to copy the files. No need to muck about with snaphots or mirror-splitting.)
