Want to move from Vbox to Qemu, how they compare?

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http://crunchbanglinux.org – I have been using Virtualbox for a long time, and want to move to Qemu. The most important features for me would be usb support , and also I need the network modes provided by Vbox: NAT, bridged network and Host-Only adapter. Sometime I need to switch between them and Vbox allows me to do this quickly from it's user interface. Does Qemu have that?I don't have a microchip with virtualization extensions, I read old post saying Qemu was slow without them, what about that now?What are the disadvantages of using Qemu?Thanks. (HowTos)