Pinterest: just another social networking site?

I recently joined Pinterest and I can't help but feel like it's just an extension of facebook but now you add so many more things than just pictures. I think there are some cool features like being able to house all your favorite recipes in one place or being able to get inspiration to design your home or wedding etc. However, my gut feeling is that people aren't always giving credit to where a photo or idea comes from so I'm not sure it's actually an effective way of marketing if people are just stealing photo's or ideas from other websites. I am active on YELP, LinkedIn, Facebook, Blogger and now Pinterest. At what point do I need to stop joining "the hottest new site"? I think I am spread across so many that I am not very involved in them. I never joined Twitter but have toyed with the idea. However, for now I will just browse everyone's pictures and wonder how they have the time?