Google officially launched Instant Previews earlier this month and we are now seeing major issues from it. A Google Analytics Help thread and WebmasterWorld thread both have reports of the Instant Previews confusing the Google Analytics and other web analytics tracking.
The issue seems to be that when someone initiates an instant preview on the Google search results, some of the times, Google will do an "on-demand" fetch of the page, executing the JavaScript many analytics packages use. So the visits are coming from Google, but they are initiated by someone searching, mousing over your listing and seeing an Instant Preview.
This can cause inflations in your visits, page views, increase in bounce rates, conversion drops, and the list goes on.
John Mueller of Google made an unusual appearance in the Google Analytics Help forum to provide some help to worried webmasters and analytics users. John said:
This is John from the webmaster's help forum. We're working on a solution for this, to prevent Google Instant Preview on-demand fetches from executing Analytics JavaScript. I'm not sure about the timeframe, but I'll drop a note here when I have more to share. Thanks for your patience.
As you can see, Google is aware of the issue and they will fix it.
John went on to add, "If you are using other website metrics tracking solutions, it might make sense to also filter that user-agent out (the detailed user-agent is listed in the FAQ page)."
So if you see major changes in your analytics in the past couple weeks, this may be why.
Forum discussion at Google Analytics Help and WebmasterWorld.
Hat tip to Adam Sherk for spotting this and sending it my way.
Update: The Google Analytics blog posted an update saying they fixed the issue at about 6:30 pm (EST). Note, they will not be reprocessing the data, so if you want to clean up your data, you can learn how to do so over here.