I think when it comes to ease of use and the social aspect Pintrest is the way to go.
I personally don't care for Pintrest though and use an app called Ember.
It is pretty wonderful. I found in the past, when I did try to use Pintest I was very sloppy with it and didn't like the process of collecting reference. Ember is much more involved but for me having a desktop app has made a world of difference. I tag and rate everything and keep it all buttoned up and specific. It is more time consuming but I have everything catalogued and saved just the way I like. It also has an RSS feature so you can check and save ref from your feed directly in the app it self.
I highly recommend it, the only downside is that you have to be on a dedicated computer to save images. With freelancing that can be tough when you come across something you dont want to lose but dont have access to the app. In those cases, I have a draft in my gmail called "To Ember" and I save everything there to later catalogue.