I may be old guy but I never get it. Why do I ever need all this virtualization stuff? I just buy a server, install CentOS, install postgresql, create another user, install java, download&unarchive tomcat and write some simple bash scripts. Voila. Everything works, everything is protected, performance is superb and I can do all that within one day. Good enough to serve few thousand requests per second. May be not enough for Facebook, of course.
And then that data center has a fire, your server is gone, your data is gone, your business loses X thousands of dollars per day, all because everything was on one server.