What’s a Petabyte?

I was intrigued by an article about building and managing a 150 Petabyte database, only to wonder what is the definition of a petabyte – a thousand or a million terabytes?

Quick research showed that a petabyte (derived from the SI prefix peta- ) is a unit of information or computer storage equal to one quadrillion bytes, or 1000 terabytes. It is commonly abbreviated PB. When used with byte multiples, the prefix may indicate a power of either 1000 or 1024, so the exact number may be either:

1,000,000,000,000,000 bytes — 1000 to the power 5, or 10 to the power 15, or
1,125,899,906,842,624 bytes — 1024 to the power 5, or 2 to the power 50.

I know that many local authorities hold terabytes of data, but has anyone out there moved into petabytes?