The idea of eyeballing the toe-in seems pretty lame to me. I have used the method that 4crawler shows in the page he linked in his message (above), where you pull off the front wheels and clamp two 36" straight-edges to the rotors on each side of the truck and measure to see if they are near parallel (slight toe-in). However now I like to use a cheap laser level and shoot my readings onto strips of plwood or drywall that I stand up in front and behind the truck.

Back in the day I used to read magazines like Road and Track where they gave a lot of specs of cars that they featured in reviews and tests. One of the specs they gave was track width, front and rear. If memory serves me not many cars have exactly the same track width at both ends. If you tried to align a car like that with the string method you'd be wasting your time -- Matt