Is the Phone Book a thing of the past?

So I had an interesting thought over the last month. Right before I ventured off on my own to start Desert DiVassistant, a very nice lady came by the house delivering the local phone books in a large shopping bag. I stopped her and told her that I don't need one as I use the online phone book. She told me she had to deliver them, so instead of having the three books take up valuable office space, I trucked them over to the annual phone book recycling dumpster at the local grocery store. Problem solved...
Then I got my city business license and my previously "do not call" phone number began ringing off the hook. Since I am in cyberspace, I answered pretty much all of the calls as they could be possible clients. One of them was from the Qwest Yellow Pages. I told the incredibly professional and kind sales person the above story and told her I wasn't interested as I have a limited space for clients. I mean, I'm only one gal and there are only so many hours in the week. I explained to her that I get all of my clients through referrals, either with networking groups or through friends, family and current clients. Besides, the listings could cost upwards of $700 per month! That's more than my mortgage (remember one gal, small house, simple needs)!
The next week, I signed a fantastic new client for just a few hours a month that wanted to do some email newsletters and update and edit her website. She also had Yellow Pages ads for a whopping $500 per month and admitted that most of her new clientele find her on the web as she has a beautifully optimized website.
So my question to you, gentle reader, is this: Are you spending $500+ per month on an ad in a book that some people will lug to the recycling center the day they get it? It is fine to spend $500 a month on marketing, but there has to be a return on investment. You should be making at least $2000 per month from that advertising expenditure. Besides, if you operate, for example, a dog grooming salon called "Zoe's", chances are, if people checked the yellow pages, they would never find you: you're a "Z"!
Helpful tip: Do you ask your customers how they heard about you? Try that for a month and keep a tally. Your customers will always tell you what you need to know about your business, don't be afraid to ask. They already like and trust you or they wouldn't be handing you their money, right?