My father-in-law has the PPC-6700 and his only complaints so far have been that it is a bit bulkier than his Treo and that the slide hinge "feels cheap" so I guess its isn't very sturdy. He says that the evdo speed is incredible though...which is another advantage it has over the current Treo lineups.
I personally use a Treo 600 at the moment and it has opened up everythign I have needed it to so far...I can only assume the 650 is an improvement
