One problem with air-drying is it can sometimes still leave spots. If you manage to blow the water off the car it works great, but any spots that evaporate off can still leave mineral deposits. In most places this probably isn't a huge problem, but the water is so horrible in some areas of Florida it can be more than just an annoyance.
Another way that works better than I'd ever imagined is to just use a low pressure water stream to sheet the water away: Wash the car normally, rinse, then disconnect the sprayer (if you use one), put the water on a steady low stream, and gently let the water flow across the car.
With practice you can "dry" large areas like your hood, roof, trunk lid, fenders, etc with water. Some cars don't work well with this method because of detail lines and curves that make the water splash and puddle more than sheet away, on others it works great.
Some vehicles, like the MGB, have a bumper strip or chrome detail line down the side that breaks up the water flow and can cause spotting under the "trim". The forced air method can quickly blow those areas dry, or alternatively a clean towel or car squeegee can dry these small areas.
Oh yeah - this method is outlined on the back of any "self dry" car wash liquid, I used Rain-X car wash for awhile and it worked great, but it also works with Mequires and several others that aren't labeled "self dry".