I wouldn't say I'm addicted to it as I am to the Internet, but like JREF (even JREF has a page), the tab is always open while I'm surfing or reading.
I swore I would never get on FB until I got an invite from an old friend to check out his pictures. In order to see his pictures I had to join, so I did. At first, I didn't communicate much as I thought it wasn't for me, but I kept my account open. Then someone from JREF "friended" me and another, etc.; an old childhood friend that I haven't seen or heard from in 40 years found me and another and another and so on, and a few from Japan, and my university, and the rest is history.
There are people I am re-connected with whom I never thought I would see again after we lost touch so many years ago back in New York when I moved to Japan. Someone from our neighborhood started a Facebook page based on that neighborhood and street name and it has enabled many of us to re-connect. We were all so close in that neighborhood, but everybody moved away and Facebook has gotten us all together again even though we are spread around the country and the world.
Overall I find Facebook to be a fascinating website with many things to do and, as mentioned above, it is very free flowing and much better than Twitter which I tried for maybe a day or two. At least on Facebook, the names are real and you know who you're dealing with and I only "friend" those I actually know from real life or from the internet, like JREF friends.
Like Tsuyoiko, I enjoying sharing, and receiving information as well as sharing pictures from my daily drive which I can upload instantly from my phone and I enjoy seeing what others are doing in their daily life. It's also a great way for keeping up with people I enjoy listening to or reading or watching on TV like Dr. Michio Kaku, as you don't have to go to their websites. It's amazing how many programs, products, interests, etc., have a page on Facebook.
It's not for everybody, but I find it a great way to stay in touch with people whom I enjoy interacting with on the internet and I do hope to meet some of them one of these days in person.