On October 5, Google.com default its search services to "encrypted search" i..e HTTPs (https://) for signed-in users, to help protecting the personalized search results.
As a result, "When a signed in user visits your site from an organic Google search, all web analytics services, including GA, will continue to recognize the visit as Google "organic" search, but will no longer report the query terms that the user searched on to reach your site."
The problem here is the "keywords used by the user on Google.com will not be available in any web analytics services. However, this dosen't apply to those who are using Google's paid advertising system (Google AdWords), as the information itself can be seen from the Panel of Adwords."
This is not good news for people who work in SEO, as a result of this phenomenon a part of the data (not yet known exactly how many) will be lost.
"To better explain this issue, Attachmedia created a nice infographic, embedded below "Keywords Apocalypse"," informed carlos vidal.
Here is the infographic: (Click to blast)