The PS4 controller is now also supported via Bluetooth. It uses the same API as the other libraries I have written, so if you have used them before, then you should be quite familiar with it.
The example code is available at Github: https://github.com/felis/USB_Host_Shield_2.0/blob/master/examples/Bluetooth/PS4BT/PS4BT.ino.
For more information take a look at my blog post: http://blog.tkjelectronics.dk/2014/01/ps4-controller-now-supported-by-the-usb-host-library/. This explains how to pair with the controller and have some background information as well.
You should also check out the readme which will always have the newest information available.
That is all for now. Hopefully this will be useful to anybody out there that wants to use the PS4 controller with the library.
Update 18. January 2014
A USB version of the library is now also available.