The sweet spot comes from users who have been to the companies during the phases about which the questions are asked. Where else can you find how much serving the Like button costs to Fb. Sure you can do a guess-estimate but how close would that be to the figure quoted by Tweetmeme CEO about their RT buttons.
There are countless such incidents. I think if the user base has some sort of expertise in an area and they "choose" to answer questions about thos domains only, that would be make it a great place for knowledge. I honestly think Quora is the lovechild of Twitter and Wikipedia. You can call it the real time Wikipedia with Questions than topics having info that I do not give a damn about.
