I use the Iphone and i have not run into too many problems as it locates the coordinates. I normally tend to start looking for places it may be when it hits about 30-20 Feet. Then i double check every now and again if i cant locate it just to make sure i don't wander too far away from the 20- 30 foot range.
Only trouble i have with the Iphone is when i go out into a dead zone and lose service. Thus no GPS. : ( Then I'm SOL. And trying to cache in New York City with the buildings cased the GPS to jump every which way.