I know that a VirtualBox VM can run on different hardware, but this doesn't help me because in my case the platform doesn't change (Linux). I'd rather like to upgrade VirtualBox from 2.2.4 to 4.x.
Will the VM start again (if that matters, WindowsXP)?
VM are easily portable from platform to platform using Import/Export capability (introduced in VirtualBox 2.2). Totally painless and works like a charm (though Windows needs to be reactivated, at least for me).