Mechanical problems with the car caused me to use my F450 as a DD over the winter. It wasn't too bad, but the advice others have given is absolutely correct. The unloaded ride quality will stir your coffee for you, which is convenient. The wider stance requires you to pay more attention to where the sides of your truck are, but if the mirrors fit, the truck fits. Traction in the rain, snow, mud, et cetera is not as good as with a 4WD single, but with 4k pounds of pin weight pressing down on the back axle, the extra two tires really grab the road. No amount of crosswind will push your truck around. Nobody will tailgate you when you're driving around town. You will not fit into the car wash, or most of the drive-thru lanes. Parking is not hard, but un-parking can be depending on what the cars around you do while you're in the store. For that reason, I park in the back of the lot and walk off all the pounds I packed on when I was driving a vehicle that DID fit into the drive-thru.
Oh, and the first time you hook up your giant FW and the truck says, "Eh - is that all you got?", then takes off like it was unloaded you will never get the grin off of your face.