How does Stack Overflow work so well with search engines?
I notice that every time I or some else asks a new question on StackOverflow it only takes a few minutes to a half hour (at max) to have the question page and subsequent answers indexed by Google.
Moreover, the newly indexed questions manage to be listed either at the top or near to the top for keywords that match the question's content - which is understandable because of a combination of StackOverflow's PR and typical content authority in question phrasing.
Where I'm dumbfounded is how StackOverflow manages to get itself indexed so rapidly and uniformly by Google? Is individual pinging enabled on StackOverflow each time a new question is entered? I don't believe a sitemap is utilized (accessing sitemap.xml results in a 404 [however that might be caused by not being a search engine user agent])?
Any insights about how StackOverflow manages to achieve such excellent SEO would be great. Even better, we could turn this into a generalized discussion about the various methods to achieve similar SEO and which tend to produce the best results (pinging on new content, metadata, blackhat - cloaking, etc.)?
I'm looking forward to hearing some interesting input on this!