I did an open house last weekend. Of the buyers that showed up, three came as a result of door hangers I circulated in the neighborhood, two came from the street signs and one came from a Realtor.com entry. The Realtor.com person said she especially liked the iPhone application. There were no visitors from a craigslist ad and none from a local Open House Day promotion.
Open Houses have several advantages even if they don't sell the home. They generate activity around the house, which reminds neighbors that the home is for sale. Sometimes neighbors are a good source of referrals, but it doesn't hurt to remind them. Open houses bring buyers to the house, which means the house could sell (and agents can sometimes turn these buyers into new clients) and open houses provide an unfiltered source of feedback about the house. I like this as a source of raw data because you never know if the feedback you get through other agents is really from the client or from the agent him/herself. In fact, during my most recent open house, I noticed an important difference between what I had been hearing from agents and what I heard from the real buyers who showed up at my open house. I'll tweak my marketing as a result.