Not sure how many of you guys saw this, but Groupon did an experiment recently where they de-indexed themselves completely from Google for 6 hours and they found that their direct traffic dropped by 60% during that time. So 60% of their direct traffic was actually from Google.
http://searchengineland.com/60-direct-traffic-actually-seo-195415
One of the reasons is that browsers are not supposed to share HTTPS referrer URLs with HTTP websites (unless instructed to to otherwise by the HTTPS site). Now, an argument could be make that it would be OK to share just the domain name since it doesn’t give away too much info, but apparently some browsers don’t share anything at all. And I’m guessing the 60% number would drop if you were running an SSL-encrypted destination site as they can legitimately get HTTPS referrer data.
Still, 60% is a big number. You gotta rethink what direct traffic really means - it’s not just bookmarkers anymore.
If you are running SSL encrypted sites and you want people to know the traffic is from you, you’ll need to add a referrer meta tag.