Thanks for porting ZFS to OS X!
I have a small BUG report.
Snapshot content is not available until you create a dedicated clone, OS X 10.8.2.
uname -v
Darwin Kernel Version 12.2.0: Sat Aug 25 00:48:52 PDT 2012; root:xnu-2050.18.24~1/RELEASE_X86_64
# kextstat | grep zfs
114 1 0xffffff7f82335000 0x19d000 0x19d000 com.getgreenbytes.filesystem.zfs (2012.09.14) <13 7 5 4 3 1>
115 0 0xffffff7f824d2000 0x6000 0x6000 com.getgreenbytes.driver.zfs (2012.09.14) <114 13 7 5 4 3 1>
# zfs list -r -t snapshot data250/backups
NAME USED AVAIL REFER MOUNTPOINT
data250/backups@snap 1.80Mi - 458Mi -
# ls -alh /Volumes/data250/backups/.zfs/snapshot/snap/
total 0
dr-xr-xr-x 2 root admin 2B Sep 24 18:53 .
dr-xr-xr-x 2 root admin 2B Sep 24 18:53 ..
# zfs clone data250/backups@snap data250/clone
# ls -alh /Volumes/data250/clone/
total 938132
drwxr-xr-x 4 estibi wheel 5B Sep 24 19:02 .
drwxr-xr-x 7 root wheel 7B Sep 24 19:02 ..
drwxrwxrwt 3 estibi wheel 3B Sep 24 19:02 .Trashes
drwx------ 2 root wheel 3B Sep 24 18:53 .fseventsd
-rw-r--r-- 1 estibi wheel 466M Sep 24 18:57 image.sparseimage