I have used cPanel from the time I started using web hosting for first time. Then Kloxo for years in all those un-managed vps I have used. Even thought Kloxo is very much like cPanel in many ways I wanted to try another free Hosting Control panel for a while now. I tried it on a vps last year but was soo confused about configuring is after installing. Installing it was a breeze but then the hard part came. There are some tutorials you can find about installing Vitualmin but most only tell you how to Installing it in your server not many tell you about how to configure the rest.
Configuring is totally different than cPanel or most of other control panels. Also in Vitualmin you called "virtual servers" for domains. I think many great for individual use but not at all for anyone in web hosting business. Nothing is user friendly for first time user. Maybe it's easy and good for experienced user but not for a newbie.
Today I have finally installed it in my new vps without a problem and also got configured it correct and testing site is up and running. I need to see how mysql works and how a Wordpress would do. But now I'm good with basics. There's plenty of more things to learn though.