After a long wait update 6 of Solaris was released a few days ago and is available for download. All new features is listed here, as i have mentioned earlier the bulk of the changes are in the major ZFS update, including ZFS boot. This is a great update to a already good OS, but i was extremely disappointed to see that they have not fixed the attach/dettach bug related to patch history yet, it have been waiting for this fix for well over a year. In this update bugid 6637869 (zone attach doesn't handle obsolete patches correctly) is fixed but a new one is listed in known issues, bugid 6710545 (fix for 6550154 doesn't always ignore older patches).
What this means is that it is still not enough to be on the exact same patch level on both machines when moving zones in a supported way, all patches have to be applied in the same way, have the same history. Otherwise it might not work. I don't know what update on attach can do for this, but that is not the point, attach is still broken.
Update, Gerald kindly informed me that this is indeed fixed in Solaris 10 10/08 (137137-09) But it is stated as an issue in the release notes, which i based this post on.
Talks I have given
5 months ago