In our area, I love seeing competitors pour money into the yellow pages. It's a huge waste of cash. In our experience, the size and color of the ad do little to enhance effectiveness in our market. A simple business listing does as well for us as the old 1/4-page 4-color ads did. Therefore we no longer put much into phone book ads.
There are many more cost-effective ways to advertise. I keep good tabs on what works vs what doesn't, and we don't repeat failed efforts. If you're just buying ads without tracking effectiveness, it's impossible to determine return on investment. "It seems to be working" means you really don't know, and that means you're just guessing.
Right now I'm locked into a contract for a promising advertisement that hasn't panned out. I'm looking forward to the end of the agreement so we can put those monthly payments towards more productive marketing. If I wasn't tracking returns, I'd be mistakenly assuming that the thing is working... and be at risk of extending the agreement. Instead, I know for certain that it is a bust, will probably always be a bust, and there is certainly no reason to repeat this experiment.