We've talked about this a bit. We believe there is a period of time—we think reasonably six months—during which you ought to be able to contact a previous user and say “Are you sure you want to leave?” That seems to be common practice, and that seems like a good business idea.
After about two years, they're gone; they're not coming back. At that point, I think it's reasonable to completely delete the data. From a business standpoint.... That's audited by checking and making sure that the person isn't actually there any more and making sure the data is truly gone.
I guess that's been mostly our approach, the six months, and the two-year window as far as permanent deletion.