I am just throwing it out there in case you simply wanted dedicated Ram or to run your own kernel when asking for KVM
It is not about dedicated RAM. I know a lot of good OpenVZ providers where I am can use the RAM I have paid for.
In this case I want to test Ruby gems with Debian/Ubuntu. So OpenVZ might work but I want to test some network stuff too. It is more about iptables, ipsec, netfilter, etc. And I have to run a MongoDB server which is not running well under OpenVZ.
I do not know if iptables and the netfilter toolset is running well with XEN? I do know that they are running with KVM.
I don't know why OpenVZ providers do not enable all modules (like iptable_mangle ipt_limit ipt_multiport ipt_ttl ipt_state iptable_nat ip_nat_irc) to allow their customers to use all iptable commands and parameters.