Google algorithm updates happen all the time, major and minor adjustments occur to the systems and formulas employed by Google even if they remain unannounced. It is important to keep up with the news and updates, working on websites which remain truly powerful online, containing useful contents and at the same time represented by links. in recent weeks and months, a lot of websites have experienced ranking drops and it is not that easy to explain happenings in all cases.
It is generally believed that contents on websites are today playing very big roles, compared with the past, and duplicate copies on sites could be among major reasons behind ranking drops. This has recently happened to tens of article directories and they have lost thousands of indexed pages and their ranks too suffered. Some websites have remained untouched or even gained better ranks because of strong links they had as well as contents on them, created in a unique way.