In the Williamsburg area, we have two types of open houses, broker opens and public open houses.
Broker open houses are held on a weekday; lunch or snacks are often served and sometimes a gift card is offered. In this area, brokers open houses can be a great networking event despite the fact that the purpose is to give the house exposure to agents who may have a buyer.
Public open houses are generally held on the weekend and are open to the public. Sometimes agents come to a public open house with buyers or if they are in the neighborhood. I often pop in to an open house to see the house and offer support to the agent who is holding the open house.
I have had some sales as a result of public open houses but have never had a sale from a broker's open.