I'm not sure if competition is great on such sites. You want one place to find answers for one topic, like programming-> StackOverflow, sysadmin -> ServerFault.
How is community going to benefit from two sites based on the exact same framework, on the exact same topic ? It will only be duplicating eachother.
Ideally, Programming Questions -> StackOverflow | Business Questions -> Startups.com. Online communities are, in a way, like physical spaces (bar, restaurants, etc). You like one over the other for different reasons: maybe the music, the drinks, the food, the host, maybe your friends hang out there. We'll see how this plays out. Competition is always good because it forces you to think more and more about how to server your customers/visitors better.
How is community going to benefit from two sites based on the exact same framework, on the exact same topic ? It will only be duplicating eachother.