I run a headless install of virtualbox with phpvirtualbox as the front end to it at home on an old N54L microserver (16GB ECC RAM, 2TB Raid 5 Array, Ubuntu Server LTS), it runs beautifully aside from one thing.
It uses VRDP (which is a bloody neat solution, I love it) to show the consoles and CTRL-ALT-DEL doesn’t actually get sent to the host.
Instead, use CTRL-ALT-END and that’ll see you right.
That took a keyboard mash and a bit of googling to find that one.