ZFS is more mature in its league then anything else on market and that is open source (or not open).
Development is being continued on open by porters on many platforms, not only Linux. (On Linux one needs to add ZFS native module separately from main Linux because ZFS is CDDL licensed (Floss, can link to other licenses) and Linux is GPL2.
Those platforms are also OpenIndiana (OpenSolaris community continuation), Nexenta, FreeBSD, Schillix, zfs-fuse, OSX, and native Linux port in progress.
And used by companies such as Joyent, Entic etc (One can get VPS servers from them)
OpenSolaris based foundation for Open distributions is IllumOS project, sponsored by Nexenta and others. (One can get payed support from Nexenta)
ZFS is being used in production environment for years (5+) and it can save you from high priced closed and hardware-tied solutions for SAN .
It can even save you form even buying high priced RAID cards/controllers.
Same pool of disks can be used on both x86 and SPARC servers.
ZFS is basically main focal point of best of what file system can give to administrators.
Oracle choose to continue developing it closed, hoping monetizing on it but one should be warned not to install SolarisExpress on their machines first with ZFS.
If you want to use ZFS pool on all supported platforms (Linux, zfs-fusa, FreeBSD, Nexenta, OpenIndiana, S11Express), one should first install eather 2009.06 or from OpenSolaris snv_134 CD (genunix.org) and Then update to both OpenIndiana dev and Solaris11Express.
That way also Linux and FreeBSD can use it - still did not tried to install and boot additional OS'es from same disk(s)/pool, but it is possible since ZFS allows MANY different OS/versions to boot from same ZFS pol, using Boot Environments

It is being reported that Ubuntu is able of booting out of ZFS disk/partition/pool with some caveats, so stay tuned
