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The only problem I see with ZFS is that you're limited with 16 exbibyte in space. Which can be filled pretty quickly if you store Chuck Norris movies.
ZFS is a 128-bit file system, which means it can store 18 billion billion (18.4 × 1018) times more data than current 64-bit systems. The limitations of ZFS are designed to be so large that they will never be encountered in practice.
I think this is a better one-line summary from the ZFS FAQ on OpenSolaris.org: