While the upgrade to 10.6 failed miserably, I used the rest of this Sunday to install 10.6 from scratch and now we have:

$ uname -rv
10.0.0 Darwin Kernel Version 10.0.0:
Fri Jul 31 22:47:34 PDT 2009; root:xnu-1456.1.25~1/RELEASE_I386
I was curious about the ZFS port from macosforge.org, since Apple removed ZFS from the Desktop versions of OSX and lo and behold it's still working:
# zpool create tank0 /mnt/tmp/file-*
# time cp -a /opt /Volumes/tank0
real	0m16.847s
user	0m0.776s
sys	0m8.703s
# zpool list
NAME                    SIZE    USED   AVAIL    CAP  HEALTH     ALTROOT
tank0                   286M    124M    162M    43%  ONLINE     -
Well, ~7MB/s is not really fast, but it's working and that's great news for everyone in need of a real filesystem. (I mean, just a few hours ago a journaled, case-sensitive HFS Plus volume wouldn't let me turn on FileVault, this is just ridiculous!)

In other news, what the heck is this?
# file /bin/ls
/bin/ls: Mach-O universal binary with 2 architectures
/bin/ls (for architecture x86_64):      Mach-O 64-bit executable x86_64
/bin/ls (for architecture i386):        Mach-O executable i386
# file /*bin/* /usr/*bin/* | grep -c ppc
I thought Apple threw those overboard with Snow Leopard?

Update I: the ZFS MacOS Forge project has been discontinued and Apple seems to kick out ZFS altogether, apparently due to licensing issues.

Update II: Another post has a few more details/speculations on this issue and someone set up a new mac-zfs git tree - yay!