Back in October, Google announced they had changed how they report information to various analytics programs. In short, searches performed on Google by visitors signed into any Google service (Google+, YouTube, iGoogle, GMail are just some) will not report any keywords to analytics programs, not even to Google Analytics.
How this affects you
Maybe it doesn't - if you aren't looking at the keywords that bring people to your website, then this doesn't change anything for you. If you are looking at your keywords and their performance (and you should be), then this will. If you use any of Google's services, it will affect behavior when you search, follow a link and then try to get back to the search results.