Flyingbronco05: The 747-200 Maintenance Manual, Chapter 30, Ice and Rain Protection, in the Description and Operation, says the following: "Wing Thermal Anti-Ice prevents formation of ice on the leading edge of the wing. The TAI system receives regulated hot air from the bleed air manifold." This regulated bleed air is about 45 psi at 350 degrees F. In flight, when the TAI system is turned on, a valve opens and allows this air to enter the ducting, which then distributes the air to the inside of the leading edge cavity. This air will always be flowing into the cavity as long as the valve is open. If the system is turned on while the aircraft is on the ground, overheat protection will close the anti-ice valves if the temperature in the cavity goes above 200 degrees F.
Chapter 30 says this about the windshields: "The flight compartment windows are electrically heated to provide anti-icing to No. 1 Lt and Rt windows, and defogging for No. 2 and 3 Lt and Rt window. Heat applied to the windows also increases their impact resistance." In flight, the No. 1 windows are maintained at about 85 to 100 degrees F, and on the ground at about 58 to 73 degrees F with the system on. (Note: Some manufacturer's windows have slightly different heat ranges).
So, to give your question a general answer, it's the leading edges of wings, windshields, and sometimes (on some airplanes), nacelles, and vertical and horizontal stabilizers that are the areas of concern, particularily during flight. Those "sprayer guys" are getting rid of ice and snow accumulation over almost all of the airplane because, simply, most of the plane is not heated on the outside, and has no other method to get rid of the ice and snow. Regards,