Images play a pivotal role when selling a real-estate - buyers get a glimpse of their prospective new homes and decide whether they are going to buy it or not. Therefore, there's even more responsibility on the shoulders of real-estate agents if they publish their work on a social networking site that deals mainly with images.
Facebook is the de facto social networking site today, but you shouldn't forget about the rest of the sites, since their services are used by quite a lot of people as well. They are somewhat different from Facebook, so there are a few guidelines to consider when using them.