In the last 5 years we've seen both Quora, StackOverflow launch and gain serious traction and Yelp has consolidated its position as a top destination for local search.
AskMeFi likely is seeing the results of going up against massively VC-backed competitors. It's hard to imagine Google's search updates were aimed at prioritizing "worthless sites".
Edit: And Reddit & Imgur have exploded. Those have probably had even bigger impacts.