I would feel that the first - hand info that we can obtain by directly participating on Fora like these, can never be replaced.....
Dont know about Twitter, but on Facebook, i havent seen many such issues being solved - it mostly depends upon the "Responsiveness" of ur friends to ur posts.
Frankly speaking, i have about 170 odd Friends, but hardly 2-3 respond, when i post any serious query or info on FB.
So in that sense, these Fora would surely be growing like anything - and add to it the Genuine "Benefits" we get by ur association with the Service providers (D2h is the live example!! I know its because u know them well, but still, we too get benefits!)
As regards FB vs Orkut - all i would say is, FB is more for just "Time-pass" stuff......if u want some serious discussions on matters of ur interest, then Orkut groups are the place to be - Let me clarify, that i am on Orkut just for the Groups, and NOTHING ELSE.
For those who feel there are groups on Facebook - let me remind that it has that 1 & only "Dull" kind of fonts, which cannot be changed......no HTML, so no "Effects" can be given....
Cant add Pics/Vids in between discussions, which adds to the interest level.
Even if there are "So-called" Active groups on Facebook, they will be least moderated - it fill be full of Spammers.
In short - i agree that FB is way ahead in all other aspects, but the quality of "Group Discussions" on Orkut is still long way away on Facebook.