Can I Have One, Please?
Is ZFS going to be available for your operating system? For [Open]Solaris users, the answer is yes; for everyone else, the answer is maybe. If you’re running Windows, probably not. For Linux, the situation is slightly more complicated. The OpenSolaris implementation is licensed under the CDDL, with which the GPL is not compatible. There are two options for supporting it on Linux. The first is to do a complete reimplementation—a huge amount of effort, and therefore unlikely to happen for quite a while. The other option is to port ZFS to FUSE and run it as a userspace process. This work is underway, but the result is likely to be significantly slower than an in-kernel version, and not usable for boot volumes. Users of Ubuntu who want ZFS support could consider switching to Nexenta, which uses the OpenSolaris kernel with a GNU userland.
Since the CDDL is a per-file license, it doesn’t affect the overall license of a project, which allows it to be used in pretty much any project that doesn’t have a license stating "all components of this project must be covered by licenses meeting these conditions." This includes FreeBSD and DragonFlyBSD, both of which have ports underway, and Mac OS X—the next version of which is expected to ship with ZFS support.