I wrote about how I didn't know how to mix Mercurial and ZFS data sets together to get a new clone on a new dataset. Dave Marker provided this insight:

zfs create pool/ws/th199096/spe-build
cd /pool/ws/th199096/spe-build
hg init
echo "[paths]" > .hg/hgrc
echo "default = ssh://anon@hg.opensolaris.org/hg/nfsv41/nfs41-gate" >> .hg/hgrc
hg pull -u

The trick is realizing that there is nothing magical about 'hg clone'.

And if at this point I want to do a closed gate, I can use my normal incantation because it wil be on the same dataset.

And I can then create a ZFS snapshot and clone that to my heart's desire.