Source: http://www.adamsherk.com/seo/10-things-that-expose-good-sites-to-google-panda/
The role of search engines is to provide the most relevant information to a user based on the keywords used to look for information. Google released Panda update to downplay websites having a huge amount of pages with thin content to further improve search results. This is a good thing; however, some sites with good content still get affected by this update making it hard to figure out the main cause of this.
Is Your Site Unshakable By Latest Panda Update
A site can still recover from this update but it will take a lot of effort to identify what part of your site is causing this. This involves a lot deindexing low quality pages, using rel=canonical, properly using 301 redirects, using 404 pages just to name a few. Remember the idiom; “an ounce of prevention is better than a pound of cure”? then it is better to make your site optimized in such a way that it will minimize the chance of your site being affected by an update.
These are some of the most common reasons why your site can get affected by panda update:
1. Slideshows – photo gallery can sometimes be considered thin especially if it consumes a big space on your page sacrificing content.
2. Syndicated content – publishing content can be a problem especially if it is posted to other sites. This could be considered as duplicate content and making such topic structure low quality.
3. Overlapping content – pages, posts, articles having almost similar topics could be considered low quality.
4. Advertisements – pages having ads above the fold which looks spam and low quality is considered thin.
5. Mobile – as more and more users shift to mobile search, web owners tend to minimize content structure thinking that short content would benefit mobile users. This is a common misconception and could also cause a site to be affected by Panda.