The link from Warner is a good starting point :)
If you only do linux:
- Requires a kernel patch
- Not really supported with latest distros (e.g. Ubuntu Lucid)
Fact is these are more luxury chroot options: you don't really have independent VM's (Virtual Machines) with their own resources (i.e. they all use the same disk).
The "disadvantage" of freeBSD jails and Solaris zones are that they are more or less proprietary and have a smaller user base.
Also with jails and zones you don't have real independent VM's.
If you want complete virtualization and have money to spare:
would be my choice. With full licencing you get nice options like:
- Thin provisiong (only diskspace is claimed you really use)
- HA (high availability: like moving VM's if the underlying hardware falls apart)
- vMotion (move VM's on the fly)
- DRS (distributed resource scheduler)
- DPM (distributed power management)
- Distributed switch (centralizes switch config).
In the end the licensing cost will weight up to reduced costs on setting up server, hardware and power consumption, depending how much you virtualize of course.
Big drawback in my opinion is vSphere depends on an administrative windows client (running vCenter).
I believe you still use templates to setup a VM (Virtual Machine) but with VMware it's quite easy to setup a kickstart server and PXE-boot/kickstart new VM's.
To be short: it all depends on your needs :)