Stack has seven sites getting at least 100,000 visits per day. One is a break out homerun (Stack Overflow obviously), and it drastically dwarfs the other sites. All but a few of their top 20+ sites are strictly technology focused, and the others are geek friendly (math and video games), so they cross over conveniently.
Most of their network is flailing. Photography is 3 years old and gets a whopping seven questions per day - that's what most of their network looks like.
Stack doesn't even remotely own the Q&A category. They own one piece of it, and will never own anything more than that, because they can't translate success in technical Q&A to other categories well. You can beat StackExchange at any given of their smaller niche sites, because they can't do them as well as someone that is dedicated to just that niche - the same reason Quora et al can't compete with Stack Overflow.