Last month Google announced the launch of a secure beta version to help all of those searchers out there who are uber-concerned with security and privacy. The secure version currently only works for standard searches and has not yet been rolled out to image search and other features.
For those who are deep into their analytics, this may have an impact on the data you are analyzing. Today you will likely see little to no evidence of this, but in the future it just may have an impact and start to confuse the heck out of you.
Any searchers who use the https version of Google, and then click through to your site, will leave no trace of how they got there. There will be no referrer data or search terms appearing in your logs or analytics software. As a site owner, you will be left clueless as to where your traffic is coming from.
As the https Google is still in early beta, you can breathe easy for a while knowing that your stats should remain fairly telling for a while, but if you start to see an increase in unknown traffic you will at least have a clue as to where some of it may be coming from.