I wouldn't say that you shouldn't use VM's, but there are some considerations. In my experiences, they work great for initial projects, short-term projects or projects that have a limited lifespan. They also work fine for small deployments. RAM Consumption is something to consider and QVS is a bit of a resource hog. That said, there are some considerations. I can't find a link to the document, but if you give me your email address, I'll email you the document I have.
thank you for your answers, my feeling also that virtual server is not suitable for large projects. I have found the document, please find it attached in this discussion. If you have more info, please forward it to email@example.com. I will keep this discussion open, the more info we gather the better.