If you are lucky enough to be test driving ZFS on you Mac, you might find this useful. The latest ZFS build from Macosforge.com has a problem where ejecting a ZFS-formatted USB disk and unplugging it will crash Leopard.
However, I wrote an Automator action [286KB download] that will sudo and run a ZFS export on all mounted ZFS filesystems, so you can safely unplug your USB drive with ZFS on it.
[robg adds: I haven't tested this one.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20081231142617289