Brent Simmons on why he performance-tests Vesper with improbably huge datasets:
I’ve learned that I’m unlikely to over-estimate the amount of data people like to keep.
I learned the same thing when running Instapaper: it wasn’t uncommon for an account to have 10,000 unread items. The highest I ever saw that wasn’t an obvious bot was just above 50,000. Even though the interface wasn’t designed to make that very manageable, I always had to ensure that the technical design could handle it gracefully.