Get a little help from your friends with GigPark
GigPark works under the same principle, except the company assumes to some extent that the people you're friends with on the site are your actual friends, not just people who happened to find you on the site. You can import addresses from your yahoo, hotmail, or gmail account onto the site to find people you know who are already using the service, and invite those who are not.
GigPark also has a Facebook application, so you could pose questions like "Who know a great eye doctor" on facebook and solicit responses from your friends directly on Facebook. Of course your friends would also have to add the application in order for all this magic to happen, which given the multitude of annoying facebook applications kicking around these days, is probably unlikely. You can make your recommendations public however, so even without adding the application your friends can read how excited you are about your new plumber.
What do you think about sites like this? Would you use it to solicit recommendations, or would you rather just call a friend and ask?