EDIT:  It seems I was misunderstood. This is not complaining that PostgreSQL doesn't scale well. It is about a case that is outside of all reasonable limits.
Part of the reason for writing this is that I hear people complain that the RDBMS model breaks down at 1TB which is hogwash. We are facing problems as we look towards 100TB. Additionally, I think that PostgreSQL would handle 100TB fine in many other cases, but not in ours. PostgreSQL at 10, 20, or 50TB is quite usable even in cases where big tables have no adequate partitioning limit (needed to avoid running out of page counters), and at 100TB in most other cases I would expect it to be a great database system. But the sorts of problems we will hit by 100TB will be compounded by the exponential growth of the data (figure within 8 years we expect to be at 1.3PB). So the only solution really is to move to a big data platform.