This is a very real issue. It happens on this site, too. A member of this site mentioned the concept of gathering intel this way a few years ago when we were meeting to sign his Will. I've always been careful and somewhat aware, but I've been more careful since his reminder.
I'm still social and friendly on the various social networking sites, but I make it a point to mention how completely variable and unpredictable my schedule is. I'm equally likely to be home on Saturday at 2pm as I am on a Tuesday at 2pm. Somebody could sit at the curb and take detailed notes 24/7/365 and still not be able to discover any pattern.
This discussion of home invasions and the techniques used by bad guys has been very helpful to me. I've already changed several things around my house and am planning a few more to guard against this potential threat. Thanks again to this valuable resource and the people who take the time to post.