What do you use virtualization on your server for?

[FakeOutdoorsman]

It's time to upgrade my half-decade old web server and much has changed since 2003. I don't have much experience with virtualization outside of desktop usage with VirtualBox, so I have much to learn in this area and I seem to learn best through examples. I haven't selected any specific hardware yet and I would like to hear some real-world experiences.

What are your experiences of using virtualization on your production server?
What serious issues have you come across?
What virtualization product are you currently using and why?

[CRIMPS]

I work for a software company. We use Virtualization for testing purposes. Our Sales Department also uses VM's for setting up Demo's for prospects. This is very useful for us in that we don't have to go through a lot of setup before a presentation is given.

I personally use a virtual machine as a second processing machine in the event I spread my personal workstation too thin. Again, this is very beneficial.

One of the main issues we had to work through was a Hardware issue. 10 virtual machines running can really eat up a lot of memory. Luckily, memory is cheap ;)

Other than that, things have been relatively smooth.

In our office we use Windows Virtual Server 2008 for our windows machines and we use Virtual Box for some of our linux machines (usually run on local machines.) I prefer Virtual Box ;)