I'm still a bit skeptical about ZFS, seen a few horror stories with it (one of the major complaints is the fact that ZFS "shouldn't" need an fsck util, but that it really does....
ZFS on FreeBSD is great, but its mostly ZFS is great compared to UFS/geom or ext{3,4}/LVM.
svn.apache.org is using it now, we caused many panics on FreeBSD 7.x with ZFS -- and lots of patches are now baked into 8.x, with all the patches ZFS has been great for apache.
Depends how you define "trickery", I suppose. ZFS root works just fine; but sysinstall doesn't currently understand ZFS (work is being done to fix this) so you can't easily set up a ZFS-only system from the install CD.
I think ZFS is bootable under OpenSolaris. Is there any reason to use FreeBSD instead of OpenSolaris if you need ZFS?
While I use Linux as my main OS, I am considering OpenSolaris for my media storage box - because I want ZFS for it. I would not consider hacking ZFS upon Linux.
Even still this is pretty content-free.
Some readable FreeBSD 8 changes I found: http://ivoras.sharanet.org/freebsd/freebsd8.html