So, I use it on my workstation because I have to also use windows and virtualbox's cross system integration is far more mature. I really only use it as necessary and it isn't running all the time.

I would prefer to use qemu, but I'm not doing anything serious with it. I'm just sometimes running a windows instance that I need to be able to easily share files with, and copy/paste across. Once virt-viewer gets there, I'll switch.

Though, to be honest, it actually uses kvm as its backend so it really isn't any less performant than qemu for this.