Late last year Solaris 10 Update 6 was released and included the long waited for ZFS root capability. Unfortunately for many customers using Jumpstart to build their systems it also meant they had to stop using Flash Archives as Sun explicitly stated that they were incompatible. Solaris 10 Update 7 didn't fix this either and zfs-discuss forum discussions seemed to indicate it would not be available until Solaris 10 Update 8 and may be available as a patch for earlier releases.
Well the day has come and the miniroot patches are now available to download from SunSolve:
Update 2009.08.20: Sun have posted some preliminary documentation on how to use ZFS and Flash.