A ZFS page page has appeared on MacOSForge.org, Apple's open source repository for projects. Not much information yet available, and it simple directs people to download the current ZFS implementation from Apple's Developer Connection site:
Well get more stuff up here in a bit, please stay tuned. In the meantime, all of you should be able to download the ZFS on OS X beta off the ADC site (http://developer.apple.com).