The Hummingbird update was released in early December and is supposed to be the biggest and most fundamental change since they introduced the caffeine indexing system in 2010. Where other updates have been a patch on top of existing software, this update is more of fundamental code change. The effects of this update are not yet clear, as only a few websites have dropped dramatically. Here are a few clues as to if you are being influenced or hit by the Hummingbird update.
infokosh 