The main things that come to mine:
DF+ has a new AF module, which:
1. No longer hunts and needs the three taps of the shutter button to get focus
2. You can make AF adjustments for a particular lens. Settings are only good for lens on camera and have to be re-entered if a different lens is used.
The DF+ works better with the IQ2 backs in that power on and off should power off both back and camera. (both DF+ and camera need to be at the latest firmware) Also if you are using a Credo 50 or IQ150, LiveView works much better in that when you hit LiveView on the back, the camera opens the mirror/shutter, whereas with the DF, you have to go through several manual steps to accomplish the same thing. It should do the same thing on a IQ260/IQ280, if you want to use Liveview on a CCD back however I am not sure if they work the same as the IQ150 and IQ250.
The DF+ new ships with a Li-On battery pack that fits in the standard handle mount. This pack can be purchased separately and will work in a DF. Either way, the LI-ON pack is a much better solution than the (6) AA battery pack.
Pretty much everything else seems the same as I recall.
Paul