We've been talking about it for years. Finally, Apple has some rock solid plans to introduce ZFS into the MacOSX operating system. As of now, plans are for Snow Leopard server to allow read/write capabilities for ZFS. No word yet if it will operate as a boot partition or not. Snow Leopard Server is supposed to debut with it's client counterpart in about 1 year according to Apple. Developers are being shown a preview this week at Apple's WWDC.
No word on whether this technology will be available to current Leopard Server users.