Solaris

i work within SEC regs and never heard of that before... have i missed something?! then again, any server we might be hosting as an exchange for example wouldn't have enough resources on a zone.

maybe other countries have this in place?

Homeland Security, financial industry in the US, just to name two.
Some applications are required to run on their own, on dedicated hardware.

In any case, at this point in time, it doesn't make much sense to implement zones going forward with the advent of ldoms and cheaper domain solutions.

That doesn't rule out running a single non global zone on that dedicated hardware which still make sense.
Zones are lighter and more flexible than domains. You can use zones in domains, they aren't necessarily mutually exclusive.

Lighter: yes, more flexible is very debatable. I don't propose to debate it but I don't agree that it is as black and white as you say. There are lots of things you simply cannot do in a non-global zone that you can on bare metal.

A perfect example of how a domain could be considered to be more flexible.

USA- the auditors did not allow a SOX-compliant and non-SOX-compliant company to be running financials/CIS on the same physical box - zones or no zones.

Your auditors may.

i wonder how that's panning out with esx servers

You are right. I should have elaborate about what flexibility I was thinking of: the ability to create zones on whatever hardware Solaris supports while LDOMs are limited to UltraSPARC T based servers, Domains to SPARC64 and other high end servers, XEN/VirtualBox/VMWare to x86.
The ability to create zones sharing CPU, memory, network and filesystem resources with much more flexibility and granularity than LDOMs or domains.
Indeed but some of them can sometimes be viewed as an advantage for zones. I for example might be less reluctant to grant some or all administrative privileges to an unexperienced user in a zone than on the bare metal OS. Most damage would definitely be far easier to recover from when done in a non global zone. For similar reasons, I would avoid putting a Internet facing service in a global zone.