Yes, Virginia, there is a limit to what Verizon will let you do with FiOS' "unlimited" data plan. And a California man discovered that limit when he got a phone call from a Verizon representative wanting to know what, exactly, he was doing to create more than 50 terabytes of traffic on average per month—hitting a peak of 77TB in March alone.
— FiOS customer discovers the limits of “unlimited” data: 77TB a month | Ars Technica
Impressive for a residential plan, but wait until you see what he does to generate that much traffic. Best bit: he's got two Solaris hosts running ZFS for backups.