It is possible for social networks to take some members from forums for some categories of forums like General chat forums.
But, I don't see social networks taking away members for forums which are about "web hosting, computers, make money online, gaming, and other categories which are less general" since it can be hard to find information abour less-general topics like webhosting on social networking sites.
I can see some validity to the point that they may take from subjects that are very broad and mainstream but for forums dedicated to computer related topics especially gaming I don't think there is much risk. Very Rarely do I see the level of discussion about video games on Facebook that I see on say Eurogamer forums.
i think the social networking sites are for people that need that online "niche" for them to spew their lives and pictures,
but on a forum i think its more people that want information about something and also people that want to give information,
the only people i know that live on facebook would never consider joining a forum because "its not public enough" like they have to be seen all the time or something,
I must admit I use social networking quite a lot as it is a useful tool for keeping up with friends who live far away and organizing big events without the need for loads of texting and phone calls etc.
From reading some of these replies, Social networks are probably making the "personal blog" where the blog owners write about their lives, share personal photos, and home videos with the world less popular because using Facebook is a lot more convenient for doings some of the tasks I listed while forums are more for discussion of current events, problems, and the media which is not as easy on social networking sites.
