To be honest I don't really think Stack Exchange and Quora are the same thing. Or, to be jargonny, "we're not in the same space."
Quora is Yahoo!Answers done really well... it's more social and bloggy, and it's for chat and subjective questions. It's kind of like Twitter in a Q&A format with long, blog-type answers. It's full of VCs and tech journalists, unlike Yahoo!Answers which is full of teenagers asking questions about reproduction in mammals.
Stack Exchange is more a reference tool... something you use when you NEED a specific answer to an actual question that actually has an answer. We're the reference section of the library, they're an awesome salon where smart people are shootin' the shit.
Actually, it depends on whether you consider volume of upvotes or volume of questions. If you look at the highest-upvoted "questions" on Stack Overflow, they most consist of things like "what is your favorite programming comic" or "is perl still relevant". These are not questions that can be answered factually; they merely ask for opinions.
Now, there are a lot more "how do i replace foo with bar in a string"-type questions, but those individually do not get many upvotes or views.
there are a few of these type questions that are semi-grandfathered in from much earlier on, but now that http://programmers.stackexchange.com is online for the more discussiony and whiteboardy stuff that isn't so code-centric, we moved the useful questions of that type there. The rest get deleted. (You can still get to them through the creative commons historical dumps, of course)
Need trumps shooting the shit any day of the week.
Stackoverflow serves a need and therefore has staying power, quora tries to serve that same need in a way that does not work well in the long run, I think it will simply blow over. Remember 'ask Jeeves' and all those other sites along the same line? Salons tend to go out of fashion after a while.
It's interesting how we're discussing this on a site that does both, serve a need and has people 'shooting the shit', maybe HN will outdo both of them one day ;)
Stack Overflow aims to be an objective reference tool. Stack Exchange is something different - it is an infrastructure for creating Q&A websites, many of them (very) subjective. Take the infamous "Programmers" Stack Exchange, for instance, the subjective little brother of Stack Overflow.
Look deeper. Quora's magic sauce is that it only shows you questions that either your contacts have interacted with or that correspond to topics you are tracking. As a result, every time you visit you get stuff that you are genuinely interested in.
Or you see no new stuff at all (if you don't have enough contacts/topics) while there are lots of interesting things going on in the other parts of quora that you have almost no way of finding out about without heavy searching.
I guess that's why they push you so aggressively to pick up contacts and topics - some of the stuff they do there is really clever, like inviting your friends to suggest topics for you if you don't have any yet.
Quora is Yahoo!Answers done really well... it's more social and bloggy, and it's for chat and subjective questions. It's kind of like Twitter in a Q&A format with long, blog-type answers. It's full of VCs and tech journalists, unlike Yahoo!Answers which is full of teenagers asking questions about reproduction in mammals.
Stack Exchange is more a reference tool... something you use when you NEED a specific answer to an actual question that actually has an answer. We're the reference section of the library, they're an awesome salon where smart people are shootin' the shit.