I like the common thread of the previous posts...expectations.
When you and your Realtor met, did you go over the marketing plan? Did you like what you saw and heard? What did your Realtor tell you to expect? That the buyer will come from an open house? Did you talk about how he does open houses?
There are some facts that might help you.
First of all, open houses do not sell houses. Houses sell houses. Open houses are primarily for Realtors to find buyers. The odds of a buyer buying an open house are very low. We do still do them, but is a buyer opts to make an offer based on an open house, it's a fluke.
Secondly, 90% of the time the buyer that purchases your home will see it with a Realtor. Not the Listing Agent. So although we do open houses, I would be more concerned about what we call "showing activity" Brokers showing the property. I would expect to meet with your Realtor weekly to review the showing feedback and update the CMA.
You should know within the first two weeks or so if the property is at the right price. If the marketing and preparation is good, and it's priced right, you should have 10-12 showings or 2 offers in the first two weeks or so. If you do not, then you probably have a pricing issue.
BTW, there are cities that prohibit open house signs. Personally I use the MLS, Trulia, Openhouseforum.com, and craigslist for open houses. I do think signs help, but in a buyer's maket most of your traffic at open houses is from buyer's being sent by their Realtor (at least in thie area).