I dunno, can't help but feel everyone is missing the point, which is not to make a Facebook clone but to increase social engagement on your forum. Sites like Facebook work because you keep your personal friends etc. on there, but forums are based around an interest, NOT around social groups.
What I envision, at least, is more of an activity feed with custom styling etc based on what happens, e.g.
brad-t started a new discussion in Style & Fashion –
RANDOM THOUGHTS: STYLE EDITION
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brad-t posted a new look
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brad-t liked a post: blah blah blah
Getting sick of writing this. But you get it. If users are posting videos or status updates to their wall, those are posts NOT being made on the forums, and who's really going to read these?
Another thing is that Facebook revolves entirely around the news feed, so there's no chance of lost focus. But this is tacking on functionality to an already existing user experience – how can you ensure that it's going to get enough attention, or worse, doesn't take all the attention?