They have for me!
A few minutes ago I was answering that blog question and I felt my answer was informational enough to post.
I sold 2 houses last year at my own open houses. One of them, was a lovely home and the seller called 10 min before I was leaving and we had had no lookers. Five minutes later she was knocking at the back door. I didn't answer so she banged louder. I excused myself from the people looking at the house and let her in and told her I had a customer there.They bought the house.
I had another house that was well priced and it sold to a lawyer and her husband from an open house. Another open house brought a client that I am working with now that I expect to sign a contract in the next few days.
In our area it isn't unusual to get 5-10 couples coming to an open house. they say 3% of the buyers nationally buy from open houses (I forget where that statistic came from, it was a few years ago). Doing the math on that you should get 1 buyer from every 7 open houses roughly.
I even had a seller come to an open house in the area where their house was, I did a CMA on their house and listed it and it sold, and they were going to FSBO before they met me and we talked.
I would never have an open house every week on a property, that makes either the seller or the agent look desperate.
I put the ad in the 2 major newspapers and put up signs. My last open house I also posted on Active Rain
They have been very effective for me for both selling homes and getting new buyers.