One wiper blade.
 

I was driving yesterday and saw a jaguar with only one wiper blade located in the middle of and at he bottom of windshield and I thought we could do that too (use a rear wiper motor of some sort and make the park position of the wiper blade vertical for less drag).

single blade
 

These usually have a pantograph mechanism to allow wide coverage of the glass.They're also usually reserved for racing cars.
Contemporary passenger cars typically have a small region of relatively high pressure at the cowl area at base of windshield to harvest fresh air for ventilation.
The windshield wipers are typically 'embedded' within this region of stagnant air,with the outer airstream skipping over.The air doesn't really snag them.
In the thread FLOW-IMAGES you can see this effect with the smoke traces.
Ford may have given the Jag something more sophisticated,as these cars when sold in Germany and Italy,can be operated on sections of the Autobahn/Autostrada at unlimited speed,at which the racing style system would have an advantage.

phord,
Several cars have a a single wiper from the factory. Citroen , Mercedes Benz and other have all used one blade for aero reasons. The usual design puts the pivot point at the base of the screen in the centre and allows the single blade to follow the airflow patterns around the glass.

From a user point of view the best design have the start point on the driver side other wise it is along time between wipes if it is parked on the other side !
The wiper motor needs to be a heavier design as well since the larger blade means more stiction and drag to overcome.

Speaking of parking the blade normally sits along the base of the screen since having it positioned vertically means it is in drivers line of sight and causing drag when it does not need to.

Pete.