I think Facebook may be taking away from some of the time some members spend on certain forums, (we run a photo contest and critique website) but having a Facebook website related to our contest website has brought in tons of new members. Every week we have 6 winners in each of the 6 categories. So I take the images with the ribbons we post in the forum like below
http://www.bytephoto.com/forums/2011...w-winners.html
Post them to Facebook as the current weeks winners, tag those photos to any members who won and may also have a FB account. All photographers online have tons of other photographer FB friends. They eventually see their friend winning, and want to join in on the fun
I also tell members that for any reason the server may go down, I will post a status on Facebook.
Try to use it as free advertising on FB. I also created a Twitter account that I post to with the wins and other things and it too has pulled in a lot of followers in the short time I have been actively using it the past 3 months