Compared to other means of advertising I have tried (any and every kind you can imagine) if done in a smart manner, for an appropriate product or service..I can think of no more effective or cose effective means of advertising.
I have spent thousands per year on phone book ads. I have spent thousands per year on radio and television. The problem is (or the problems are) that the customer has to be listening, looking at that page or channel. The customer has to be receptive (and not tuned out because they are overly exposed ot advertising) The ad may appear in areas that you are not intereste in servicing. The list goes on and on .
I recently found this article which states some interesting numbers http://www.esigns.com/cost-effective.html
as to the cost of banner advertising. I like those costs MUCH more than ALL other forms of advertising I have tried.
However, I have had some royal flops in regards to advertising with signs and banners as well. Almost all attributable to my ignorance and not researching the subject.