One of the things that keeps me from going to Facebook is the huge amount of false information that gets forwarded by people without checking validity.  Then there are the deeper, more entrenched urban legends.  Here is a fantastic blog post on the subject of model releases and property releases.   Great article - lots of good research.

Model Release Myths

"While it's true that model release are necessary for certain situations, the actual laws about these issues are deep and complex. As rumors and hearsay perpetuate on the net, the over-simplification has resulted in virtually all the "advice" and conventional wisdom about model releases to be entirely wrong. And the reason why these myths perpetuate is because they cause no harm. No one ever got sued for having a model release. So, people follow the advice because they (and others) seem to be safe, perpetuating the myths."

Do couple this information with manners.  Even if you do have permission, you won't get invited back if you piss people off.