Open house guide, where are you?

I cannot seem to find an online Open House guide that comprehensively taps a national database of houses to visit on Saturday and Sunday (throw in broker tour stuff, too, OK?).
I like the UI on OpenHouse.com but it is thin on the data side. A couple of years ago, Realogy purchased the URL and has been slowly filling it out with listings.
Since newspapers have had a print monopoly on this important consumer feature for decades, it seems like Classified Ventures would be perfectly suited to offer this. Of course, most local newspapers offer the OH feature.
I am sure the Zillowites are on this, or maybe the Trulia boys who have perfected the art of [legally] scraping listings.
Over the years, I have gotten no less than 30 biz plans from start-ups (FYI: the biz plans are peaking again, almost comparable to 2000) offering online open house guides. Of course, the challenge isn't in building the technology application, it is obtaining the data -- too many sources. And what are the economics?
Help me out. What's out there? Any cool open house feature sites, new tricks, etc.?

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