Perhaps as an official start to the spring selling season tomorrow is the start of Open House Weekend when realtors all over the area are doing what they do every spring weekend and holding open houses. Maybe they're going to do it better this weekend? Who knows. But, there are almost four thousand open houses happening in the DC area over the next two days (the number keeps rising every time we refresh). Here is a list of all of them, but you can filter by the usual categories on the tool bar on the left hand side to find places with your criteria.