Since Quora just went public, I decided to have a look around and found certain topics like Gmail that contained questions that would be great for the Web Apps SE-site.
However, would it be considered plagiarism if I simply asked the same questions on the new site?
Edit: I would only look at the titles for an interesting question to ask, so if I write my own question body, it's not plagiarism in the real sense of the word. However, it's probably not really polite since if we are better indexed or have a better PageRank, we would steal some of their attention.
In response to Jeff's answer: how should I attribute to the sites? Simply mention I found this question on Quora and link to it?