How to install FreeBSD 8.0 using only ZFS partitions is a step-by-step guide for install FreeBSD 8.0-Release on to ZFS at  What make this how-to different from many others is it works!
I followed the how-to to install FreeBSD 8.0 Release in to a VirtualBox VM and it worked on the first try.  I haven’t try installing any ports or updates to see what happens.  One step at a time.