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.
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:
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.
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.