Input options (XID SDL branch)
You can use -device usb-xbox-gamepad-sdl,device=<name>,index=<index>,bus=usb-bus.0,port=3.2 to use your Xbox 360 controller as input option (Requires a hub on port 3. See Input Options). <name> is the name of your input device. It's commonly "Controller (Xbox 360 for Windows)" on Windows and "Microsoft X-Box 360 pad" on Linux (make sure to include the quotes!).
To find out the name of your device simply leave out the ,device=<name> part and check the output.
<index> should be 0 if you only want to use one controller of the same kind. If you have multiple devices with the same name you can use the second controller by using index 1.
This is a temporary solution. Later versions will support mapping buttons and keys however you like. The button mapping might change again for the Black and White button until then.
Until we use a more recent QEMU with SDL2 there won't be any force feedback support (which is already implemented, but untested).