I use LinkedIn on an almost daily basis to establish and maintain connections with clients, crew, subjects, other photographers and people I meet during portfolio reviews or other events. I wish it had been around years ago when I first started showing my portfolios because it’s an incredible tool for staying connected with people, especially if they change jobs. I can’t tell you how many people I met with 5 years ago that I now have almost no way of tracking down, especially if they have a popular first or last name (or both). I would be surprised if freelancers in any field were not taking advantage of this great connecting tool, especially photographers. I have had people contact me through the site who were interested in hiring me. This makes sense. As I have begun keeping better track of all the requests that come for my services, about 80% of them come from referrals or previous clients.
My philosophy is that everyone in my network should have some sort of connection to me in the non-virtual world. Even if its just a meeting or a request for a quote that doesn't pan out, it’s better than just connecting with people I don’t know. All the more reason to get out from behind the computer and get some actual face time more often.