I feel doorhangers have there place. They should not be your only form of advertising, however they should be part of everyones who is still trying to grow. IMHO you should target 5 to 7 houses closest to a client you already mow at least a couple times a year.
This of course gets your name out in a area that you are already, so you are helping keep your route tighter, but also letting them see them a couple time a year reminds them that you are already there if there current guy messes up.
Not the best form but one I think still think plays a essential part of your advertising if you are actively trying to grow.