Google recently announced that it will enable secure search for all the login users. More HTTPS usage is in general a good thing, but it does have a side effect:

Apparently RFC 2616 specifies that:

Clients SHOULD NOT include a Referer header field in a (non-secure) HTTP request if the referring page was transferred with a secure protocol.

Makes sense.

HTML5 also has a new "noreferrer" (with the correct spelling this time) that can be used to instruct the browser to never send HTTP_REFERER to the destination URL.

For my own amusements, I can still correlate those visits from Google with the landing page to guess what people are interested in when visit, so it's not too big of a deal.