In customer presentations about Zones there is an always reoccuring questing. How huge is the performance impact of virtualisation. Most of them have some experience with VMware and it´s rather high impact (unfortunately the VMware licence conditions don´t allow independent benchmarks, so there are no real public numbers about this) or with other virtualization technolgies. Most of the time, they don´t believe that the impact is almost ignorable. We ran some benchmarks with SAP-SD, that clearly show that zones have only an impact of less than 1% (even less than the 3-4 % i use as a safe harbour statement in presentations).
Apropos Zones: There are two interesting pages around this topic: At opensolaris.org you can look at the state of certain extensions to the Zones implementation. And at sun.com you find a guide about the integration of ZFS and Zones.