Before getting started on the benefits of ZFS, it should me mentioned that ZFS is supported on Linux, Illumos, and even Mac OS X. My personal experience working with ZFS comes from FreeBSD, where it has been available since 2007. I can’t speak to the stability on other platforms, but on FreeBSD it is rock solid and has been production ready for years.
The features of ZFS are mostly centered around data protection and administration. When I write a file to a drive, I’m expecting to be able to get that same file back again, in the exact same state that it was when I wrote it. Unfortunatly, spinning rust hard drives are notorious for being unreliable, so much so that I never put just one in a server, there are always at least two in a RAID 1 mirror. ZFS addresses this issue by including a checksum of each block of data written for the entire filesystem. By having the checksum, and checking it each time a block of data is accessed, ZFS can tell if the data has been altered or corrupted. Once ZFS is aware of an issue, there are a few ways that it can automatically correct the problem, depending on how the hardware is configured.