For years I've been asking software developers to actually create what end users want, not what admin-geeks want to play with. Facebook and Twitter have done that. I can give a lot of examples but don't want to bore everyone.
Bore me. I develope software, and never in a trillion years would it have occured to me to build Facebook and/or Twitter, both of which I don't use because they bore me beyong galaxy's gravity.
You want it? Pay.
Which sort'a drags back to the question of whether-or-not Facebook and Twitter threatens forums.
I guess it basically depends on your IQ.
Did you know (I learned this from my stats prof, which in Canada is normal, but which in the US is idiotically expensive, such that Harper is following the pide-piper of making it as hard in Canada as in the US, in spite of the fact of being Canadian is supposed to mean thing are *not* going to be as crazy nut-grabbing as south of the border) that couples are always within 5 IQ points of each other? She might be crazy, but she's as smart as you.
Friends are always within 7 IQ points, and aquaintences are within 10 IQ points.
Out of reach is when it's more than 20 IQ points. At that point everything breaks down. The US Army did a study back in the 40/50's when intelligence was respected, and they found it was impossible for a seargent to command a platoon comprised of recruits wityh more that 20 IQ point difference.
Nobody was suprised when a dumb seargent could not command smart recruits, but the suprise was when they put a seargent in charge with 20 IQ points smarter than the recruits.
He couldn't command them. Something about their way of dancing around like monkeys he totally didn't get.