There have been rumors that Leopard (Mac OS X 10.5) would include support for ZFS and it appears, with the latest preview from Apple (see Ars Technica), that that rumor is reality.
This has caused an unsurprising fuss and state of excitement in developers and users. Everybody knows that HFS and HFS+ (the current filesystem choices) are really bad. They are comparatively very slow and inefficient and archaic from the perspective that they put some interesting restrictions on how files, file naming and individual partitions of a hard drive are used.