Which OS should I pick for ZFS compatibility?

I'm in the process of building a new file server, and I want to use ZFS in a RAIDZ configuration with four 750 GB drives. The obvious choice is OpenSolaris, but I'm wondering if I should consider any other ZFS-compatible OSes, such as Nexenta OS or FreeBSD. I've heard that FreeBSD is not completely compatible, but that it's gotten better in FreeBSD 8.0. Nexenta looks interesting, since it's just the Solaris kernel with a modified Ubuntu userland. Does /prog/ have any advice?

advice?
go back to /g/ please
also as a system administrator whose dba is using zfs in production, i'd say it's still not ready for prime time