>This project is probably irrelevant for Linux, since there's no way to get ZFS accepted into the mainline kernel. The main benefactors of this project are *BSDs and various OpenSolaris forks.
On the contrary, this is likely to be particularly beneficial to Linux, as it represents ZFS as a standalone project, rather than a part of illumos. One of their goals is a greater separation of platform-specific parts, and an emphasis on improved portability and co-operation between the different ports of ZFS, which should reduce the work required to keep zfsonlinux up to date with upstream. (See http://open-zfs.org/wiki/Reduce_code_differences and http://open-zfs.org/wiki/Platform_code_differences)
>Anyway, btrfs is clearly a replacement for ZFS on Linux. It doesn't have all the ZFS features right now, but it'll probably get them in the near future.
We've been hearing that for five years now. Currently it's nowhere near feature-complete, progress is slow, and people are regularly losing data. I have a reasonably high degree of confidence that there will *never* be a day that it catches up to ZFS.