re user engagement the "threshold" for submitting a funny picture or pun anonymously is much lower than writing a well-written answer in your full name.
quora has about 650k questions in total, most of which are unanswered and in general ignored. my estimate of answered questions puts it at 80-90k.
as for user-base, the churn rate is huge with the majority of users following 2-3 topics before leaving the site forever. there is subset of users who generate all the content and value of the site.
lets look at some numbers:
Yishan Wong: Answers 1457, Question 760
Jeff Hammerbacher: Questions 1092, Answers 1041
Jan Mixon: Questions 802, Answers 4101
Michael Wolfe: Questions 9, Answers 1088
Mark-Hughes-1: Answers 1294, Questions 48
power-laws ahoy.
it's good source of info on startups and the tech scene, which makes it more like a popular discussion forum
than a social network. I don't see this growing to millions
of active users unless it tries to take on Yahoo! Answers.
i believe the quora team acknowledges this, and with the introduction of boards they're trying to redefine the site to be some kind of textual pinterest.
this sounded quite pessimistic, it's actually the site i visit the most and i hope they continue to grow without
comprising on the quality.
there's not many master students doing a pure stats degree at the university of Oslo, and as a consequence some courses are offered only periodically, but you can still "self-study" them for credits, and there anyways enough related courses in fields like computational finance, numerical analysis and machine learning.
regarding moving back to the US: you can always take a local job in the oil industry or perhaps in a global company like mckinsey and then move back when you have some real experience (it should be easy to get a job here)