To help you keep things simple, let's break down what the virtual network is for a moment. VLANs are a great place to start because they illustrate the core principle of almost all virtualization: an abstraction of function from physical resources. We can take 24 ports on a switch and actually divide it into 12 virtual two port switches. If you are wondering when or why you would ever do that, then you are walking down the network virtualization path right next to me. The current definition of network virtualization amounts to creating a profile of an Ethernet switch port, either within a set of switches or running as software within a virtualization hypervisor, and enabling this profile to be moved around your network as you move virtual machines. Some variants of this definition, like VPLS, revolve around flattening the network to achieve approximately the same goal, which is a very wide, dynamic layer 2 topology. Both of these try to solve the problem of being able to move virtual machines between VMware ESX hosts, for example.
If you want to know if network virtualization is going to help your network, you should consider which of the following seem the easiest and least expensive:
* Configuring VPLS in your network
* Configuring dozens of port profiles that are attached to each VMware host and then swapping out the VMware Distributed Virtual Switch for a 3rd Party switch API, and then setting up the network management software to handle the monitoring and maintenance of these profiles and their mapping to physical switches and ESX hosts.
* Changing the IP on a server when you have to bring it up at a different site and updating your DNS servers to reflect the change.
To achieve a virtual network you might provision VPLS or use port profiles, or in some cases, both. They are not simple tasks and require significant time investment as well as additional costs for equipment upgrades and management software upgrades. The major benefit of doing either is to facilitate moving VMs around your network without needing to do option 3. Option 3 seems to me to be the least arduous and least expensive option, even though it requires some manual work when you need to move a virtual machine. In the end, all of these accomplish the same goal of bringing a VM online in a different part of the network.
Our clients, who probably look a whole lot like you, are only moving VMs if they absolutely must. Their networks are not going to benefit enough from the complexity of network virtualization to make it worthwhile. Your environment may be different, and in that case you may find great value in network virtualization. For everyone else, don't be intimidated by people who talk about network virtualization as if it is some new and great way to improve your life. It is not new, it is pretty good, and it really won't help you much right now unless you have very specific needs. If you want to improve your life, take a quick look at the duplex settings on the interfaces that connect to your ESX servers and make sure that you aren't getting thousands of errors on them. Remember, keep it simple unless you have no other options!