Sites like these are, in my opinion, the scourge of the internet. There is a lot of talk nowadays about curated search engines displacing machine-generated search engines but I tend to think this goes too far. A search engine that could reliably determine the authoritative source of duplicated content and only include that source would be killer. Seems within the realm of possible... Anyone working on that?
We're doing something along a similar vein for LazyReadr. The idea is to merge news about the same story together, an important step from there will be deciding which is the authoritative source to display. Going from that to effective search isn't a large leap.
Also, in many cases (eg. this one) the duplicated content even links to the original source, so even simple pagerank should put stackoverflow significantly higher than its duplicates.
