This topic is very essential in this day in age. If you look at my profile, you will notice that I had raised this issue long time ago. In fact, I am astonished at the slow to no response from most webmasters to the alarming rate at which FB is growing.
My own site, which has been online since 1998, has suffered a lot from this. A lot of my users spend so much of their time on FB, and very little on my own. I still gets lots of people visiting, but I have to admit, I also have lost a lot. And there is nothing else I can attribue this to, other than to FB. I have seen it, observed it and analyzed it.
The question is, what do you do about it? will you let one network control everything and for tens of thousands of webmasters to just give up and watch their website and income evaporate? For me, I have done many things to stop the bleeding, and innovate with the times:
-Ironially, you have to embrace FB, but not go crazy. I have a Twitter and FB accounts (including a FB group) and I use them both to link to link to important new sections and links on my website. It does help in getting visitors to my website
-At the same time, webmasters should band together and stop sucking up to everything FB.
-Embrace rival technologies such as Twitter and hopefully the new and rumored GoogleMe social network
-Keep your site as up to date as possible. If you have at least 100 friends on your FB network, chances are you always see new stuff when you login. Why would they come to your site instead if your site only gets updated once every few days?
-Encourage your own site users and friends to promote your website on FB. Tell them to share any interesting things they find on your website, back on FB, to attract more visitors.
Unfortunately the FB threat is here to stay for some time. We just have to be ready to both fight and embrace it at the same time.