Comparisons -> Adwords vs. Yellow Pages

Google Adwords	Yellow Pages (print)
You pay only when someone is interested enough in your ad to click.	You pay no matter if anyone sees your ad or responds to it.
You control budget for each day. Can raise, lower, or pause on any day.	You pay a large fee for an annual ad.
You can have custom ads for different searches - no charge!	Ads are not custom. Multiple ads means multiple charges.
Don't like the ad you're running? Change it!	Once it's printed, that's how it will be for a year.
Now a majority of searches for services are done online.	Once dominant, but not anymore.

The one thing I will give to the Yellow Pages is that it was dominant for a long time for a good reason - because that is where people went when they needed a service. This is exactly the person you want your ad in front of - the person shopping for a therapist right when they need it! Now that person is searching Google rather than the Yellow Pages.