I've very recently discovered Pinterest, an enjoyable and easy way to literally pin your interests onto a virtual pinboard.
If you don't already know what it's about, I'll give you a quick summary.
Essentially, you create 'boards' and name them according to how you would like to categorise photos and subsequently add photos directly from a site into those boards. For example, you can make a board called 'cooking' and then fill it with all sorts of delicious food recipes and food porn.
The way you add photos onto your boards is very simple; you add a bookmark to your bookmark bar, and when you come across a photo you take a liking to on a website, you simply click the bookmark button and a page will come up allowing you to both choose the photo and place it into your desired board. I told you it was simple!
As you can see I'm still playing around and in the beginning stages of setting it all up (with the exception of my 'wish list' board haha), but now that we fiiiiiinally have internet as of this morning, those boards will be filled up very quickly.
I'm not entirely sure about the social networking aspect of Pinterest, but I believe you can follow other users and 'repin' their photos. I'll have to experiment more with the site to grasp it fully. If anyone is familiar with this let me know, and make sure you tell me your usernames so I can check them out.
Oh, my username is 'luarrr'. Yes, somewhat reminiscent of a lion's roar but alas, 'luar' was taken, as was the word with two 'L's' so I had to compromise and use three, as with my blog url. Oh pooh!