Quora is Q&A+wiki+follow-up questions. Stack Overflow pioneered Q&A+wiki, and Quora's follow-up question connect up individual Q&A in a way that's similar to Yoomoot.
Quora is less innovative than Yoomoot and yet it has received a lot more buzz. That's because it was founded by ex-Facebook employees and got big money in funding.
With more publicity they get more funding which means a more effective Q&A community.
They were founded in June 2008, have a big team and took $11 million in funding.
We have only two proper team members (and a hired nearly full time developer) and have £5,000 funding.
yoomoot has the following features, which Quora doesn't have, which mean that big complex discussions are quick to get an overview of:
These differences mean that long complex discussions on Quora (which I unfortunately haven't been able to find examples of yet) will not to be quick to get an overview of: most of the nitty-gritty back-and-forth, i.e. the meat of the discussion, will be buried in comments underneath answers.
yoomoot has plans for more social elements but unfortunately they haven't been implemented yet. Quora certainly does better on the social-rewards and engagement with friends front.