There was a great article holding a short the history of Zones under Solaris 10 on a version by version release.
Solaris 10 11/06 (Update 3)The benefits to Zones are many, but a few include: zero cost, incredible density on a single OS instance (up to 4000), and virtually no overhead.
Zone move and clone
Privileges in zone configuration
Solaris 10 8/07 (Update 4)
Upgrades, Live upgrades (ZULU)
IP Instances (dedicated NIC/separate TCP/IP stack)
Resource setting for memory/CPU
Solaris 10 5/08 (Update 5)
Dry run of zone migration (zoneadm -n)
CPU caps for zones
Solaris 10 10/08 (Update 6)
Update on attach
Default router in shared stack
Full ZFS support for zones
Solaris 10 10/09 (Update 8)
Turbo-Charged SVR4 Packaging
Zones Parallel Patching
Solaris 10 9/10 (Update 9)
Zones P2V (Physical to Virtual)
Host ID Emulation
"Upgrade on attach"
Solaris Zones are an essential part of any cost effective data center when performance managed services for external customers.