Ah, I so love ZFS for usability (can't really say for a production Oracle system), but you can see it's beauty right here. I needed more swap for my system while linking Oracle 11.2 binaries on x86-64 opensolaris 2009.06, the initial installation allocated only 512MB. The storage for swap comes from a ZFS storage pool, called "rpool" by default. To extend it, I followed these steps:

root@opensolaris:~# zfs get volsize rpool/swap
NAME        PROPERTY  VALUE    SOURCE
rpool/swap  volsize   512M     -
root@opensolaris:~# zfs set volsize=2G rpool/swap
root@opensolaris:~# zfs get volsize rpool/swap
NAME        PROPERTY  VALUE    SOURCE
rpool/swap  volsize   2G       - 

Voila! That's beauty.