Well just the way it works/Navigates, for example you if you put a cd full on mp3s in the unit you cant search all the songs and pick the one you want, you can only type in a number or flick through 1 by 1. The graphics also are not that great but i now download music videos and burn them to vcd looks well smart.
The other minor issue i have is the fact that the front of the unit comes of for securiety but pioneer to not supply a case to carry it in at the moment i am using the case from my oakley sunglases.
Dont let me put you off despite these little issues all in all its a very impressive peice of kit. As i say i have no regrets in buying it and am very impressed with it. If your looking at the Avic X1 its even better but was VERY expensive when i bought the 6500DVD i notice now you get get a really good price on it.
I say go for it you wont be sorry!!