We use the YP's. Didn't always. When it was just me I kept it to a bare minimum, an in-column text ad. When the wife started working with me and we got serious about increasing sales she started taking out display ads. At one point we were in six or more directories. Some did well, some didn't, overall it was a net gain.
It takes a little thought. You really need to look at the current directory, take your best guess at what it's gonna look like next edition and do what you can to get the best placement for your money.
Do a little homework and see what directories are available. We got into a lot of the smaller community directories. They're often a fraction of the price. It sounds like ad sales are off, like everything else, and from what I'm hearing they're willing to wheel and deal to get your business. And, don't let the YP people design your ad.
We don't put all of our eggs in a YP basket, but a YP presence is something I personally wouldn't want to be without. For as convenient as the Internet is, YP's are still the quickest, easist way for a lot of folks to find a local business. The younger generation may be using them less, but I'm betting the older generations will continue to use them.