ZFS is in, ZFS is out… OK, so now we know that ZFS file system support is in Mac OS X Leopard. The read/write support was just seeded to developers according to reports online and no one but complete nerds will notice unless Apple makes it the default file system. The WWDC build of Leopard still has journaled HFS+ as the default file system.
Man oh man, nothing like writing about file systems early in the morning to start the day.
ZFS Read/Write Developer Beta for Leopard [MacRumors]