I haven't made, or even talked to anyone who's done this, but what the hey... it's Sunday, figured I'd toss out my two cents for whatever it's worth.
All the local business owners I've worked with and spoken with have gone a few bouts on the phone with the directories. This was a fresh idea years ago, but now there's a dozen+ different directories reaching out, some of them fairly aggressively. So yeah, it does work as a foot in the door (Hi, this is Yelp, etc. etc) but it doesn't get you under that shield of skepticism that local business owners have all had to foster over the years. Marketing ourselves is a lot harder than marketing our clients, in part just because our audience has been burned so many times in the past. Most dentists don't have to put up with that level of skepticism (how do I know you're a REAL dentist, and that you're not just going to mess up my teeth and waste my money?)
In my own experience with marketing, seems like the best plans all have to fit a very particular equation. Goes something like this: how much money will it cost, how much time will it cost, how quickly can you test it and back off if it doesn't look promising, how congruent is it with everything you've already got going for you, etc. Fail fast, fail quick. If all you're looking for is a new way to bump up lead gen, you could try a million other things that you could cook up and have out the door in a month's time. If this is a plan that will take 6~12 months before you can fully decide whether or not it's time to pack in your chips and try something else, that's a ton of lost opportunity for smaller outreach... and even if a directory DOES get your foot in the door, you're still going to need to have a solid strategy for hooking them in the rest of the way. The big directories have whole boiler rooms full of sweaty, experienced cold callers, slaving away on consistent, targeted outreach. You'd be making sales that way too with that size of a sales force, even if you didn't have their hook. You just need the right offer, the right approach, and all the rest.
That doesn't mean it doesn't work though, just means that the opportunity cost for testing it out sounds a lot higher than other, easier things (Direct response to the right list, through the right medium, with the right front end offer and sales pitch) especially if you're a small shop, and you're just looking to build up to a dozen healthy, awesome clients on retainer. I think a lot of small shops grind away months and years on 'plans' that all involve work to avoid actually spending time in the trenches, talking with their audience as often as possible.
Obviously if you've already got a dozen stable clients and you're looking to start scaling, disregard all this. I'd still test webinars, books, and speaking engagements before I'd test a directory site though, just because they'd be easier to measure results, test, and iterate on. (Though the book would only be in that category if you've written a bunch already).
I'd still love to hear sometime what Colan and Joy have to say about it though.
Edit: just realized this was an old thread that got revived, my bad. Ah well, rant stands.